FORM 6-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Report of Foreign Private Issuer

Pursuant to rule 13a-16 or 15d-16 of

The Securities Exchange Act of 1934

For the month of December, 2015

National Bank of Greece S.A.

(Translation of registrant’s name into English)

86 Eolou Street, 10232 Athens, Greece

(Address of principal executive offices)

[Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F.]

[Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to rule 12g3-2(b) under the Securities Exchange Act of 1934.]

[If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): 82-              ]

December 8, 2015

Notice to holders of the 12,639,831 outstanding non-cumulative preference shares, Series A (the “Securities”) represented by American depositary receipts (the “Preference ADSs”), issued by National Bank of Greece S.A. (the “Issuer”)

Background

On 31 October 2015, the European Central Bank published the results of its Comprehensive Assessment in respect of the Issuer, which indicated a capital shortfall relating to the baseline scenario and the adverse scenario of the stress tests carried out. The Issuer is required to remedy such capital shortfall by December 11, 2015.

The Issuer has undertaken a number of actions to cover the shortfall identified in the Comprehensive Assessment by generating Common Equity Tier 1 capital and strengthening the Issuer’s capital position.

In addition, on December 3, 2015 the Issuer made a formal request for State Aid to be provided in order to allow the Issuer to meet the residual capital shortfall arising from the adverse scenario of the aforementioned stress tests.

European State Aid rules and relevant powers attributed to the Hellenic Financial Stability Fund under Greek law

The Issuer notes that, pursuant to European Union law, if State Aid is required to be provided in order to allow a bank to meet any relevant capital shortfall, then, according to the Communication of the European Commission on the application, from August 1, 2013, of State Aid rules to support measures in favour of banks in the context of the financial crisis (the “Banking Communication”), burden sharing needs to be achieved through contributions by holders of equity, hybrid capital and subordinated debt of the bank, in order to reduce the capital shortfall to be met by State Aid to the maximum extent possible.  This is the case even if no resolution action or crisis prevention measure is taken in relation to the Issuer at the relevant time pursuant to Directive 2014/59/EU of May 15, 2014, which provides for the establishment of an EU-wide framework for the recovery and resolution of credit institutions and investment firms (the “BRRD”), as implemented in Greece pursuant to Greek law 4335/2015 (the “BRR Law”).

As they relate to the Issuer, the requirements of the Banking Communication mean that, to the extent State Aid is required for the purposes of remedying the capital shortfall of the Issuer identified in the Comprehensive Assessment, even if no resolution action is undertaken under the BRRD or the BRR Law, the holders of capital instruments, including the Securities, will be required to contribute towards strengthening the Issuer’s capital position before State Aid is provided to the Issuer.

The burden sharing requirements imposed by the Banking Communication have been reflected in Greek Law no. 3864 of 2010, as recently amended and currently applicable (the “HFSF Law”), which attributes to the Hellenic Financial Stability Fund (the “HFSF”) the ability to provide State Aid through subscription to common shares and other securities issued by a Greek bank, subject to the mandatory write/down and/or conversion of the capital instruments and certain other liabilities of the bank  in question. The Securities form part of the share capital of Issuer, are governed by Greek Law and are treated as Additional Tier 1 capital instruments pursuant to the grandfathering rules of the Regulation (EU) 575/2013 (the “Capital Requirements Regulation”).  The Securities are therefore eligible to be subject to the mandatory conversion of the HFSF Law.

1

A Cabinet act, following recommendation by the Bank of Greece, was issued on December 7, 2015 (the “Cabinet Act”) further to the Cabinet act issued on December 5, 2015, to implement the Burden Sharing Measures so that the request for State Aid is satisfied. The Cabinet Act and the Cabinet act issued on December 5, 2015 are included as exhibits hereto, together with unofficial English translations thereof. The Cabinet Act provides for the determination of the class, type, rate and amount of capital instruments and liabilities which will be subject to the Burden Sharing Measures, on the basis of a valuation of an independent auditor, appointed by the Bank of Greece.

The application of the burden sharing rules under the HFSF Law will result in the conversion into newly issued common shares (the “New Shares”) of the Securities at the rate of conversion determined by the Cabinet Act, being 100 New Shares per €100.00 in outstanding nominal amount (liquidation preference) of the relevant capital instruments. As the Securities are U.S. dollar denominated, an exchange rate of 1.0579, which was the European Central Bank euro/U.S. dollar exchange reference rate as at November 30, 2015, shall be applied. As a result, each of the Securities, having a nominal amount (liquidation preference) $25.00, shall be converted into 23.631723 New Shares by the conversion.

The New Shares, being common shares of the Issuer, will be represented by additional American depositary shares representing the Issuer’s common shares (CUSIP#: 633643804) (the “Common ADSs”) issued pursuant to the relevant Deposit Agreement among the Issuer, the Bank of New York Mellon as depositary and the holders of ADSs, as last amended on January 22, 2010. Delivery of American depositary shares representing the New Shares to holders of existing Preference ADSs in exchange therefor will be made promptly on or after December 11, 2015, in accordance with the notice and procedures of the Preference ADSs depositary, the Bank of New York Mellon. Holders of record of the Preference ADSs will receive a letter of transmittal from the Bank of New York Mellon, which will detail how holders of American depositary shares representing the Securities may surrender their certificates in exchange for American depositary shares representing the New Shares.

Delisting and Deregistration of existing Preference ADSs

Trading in the Preference ADSs on the New York Stock Exchange has been suspended by the New York Stock Exchange as of November 27, 2015.  The New York Stock Exchange has notified the Issuer of its determination to delist the Preference ADSs and commence delisting proceedings.  The New York Stock Exchange will file a Form 25 with the Securities and Exchange Commission (“SEC”) during December 2015 to effect the delisting and deregistration of the Preference ADSs. The delisting is expected to be effective 10 days after filing Form 25. The deregistration will become effective in 90 days after the filing of Form 25 or such shorter period as may be determined by the SEC.

Trading in the Common ADSs on the New York Stock Exchange has been suspended by the New York Stock Exchange as of November 27, 2015.  The New York Stock Exchange has notified the Issuer of its determination to delist the Common ADSs and commence delisting proceedings. Management is considering all available options in respect of the listing and future trading of the Common ADSs.

The Issuer intends to continue to fulfil the reporting requirements under the Exchange Act which are applicable in respect of the Common ADSs.

US federal income tax considerations

The parties will treat the exchange of the Securities for Common Shares as made pursuant to a “plan of reorganization” within the meaning of Sections 354 and 368 of the US Internal Revenue Code of 1986, as amended, and the US Treasury regulations thereunder.

*           *           *

2

This release is not an offer of securities for sale in the United States.  The securities to which this release relates have not been registered under the United States Securities Act of 1933, as amended (the “Securities Act”), and may not be offered or sold in the United States or to, or for the account or benefit of, U.S. persons, absent registration or an exemption from registration under the Securities Act.  There will be no public offering of the securities in the United States.

This release contains certain forward-looking statements. These forward-looking statements involve risks and uncertainties that could significantly affect expected results and are based on certain key assumptions. Many factors could cause actual results to differ materially from those projected or implied in any forward-looking statements. Due to these uncertainties and risks, readers are cautioned not to place undue reliance on such forward-looking statements, which speak only as of the date of this announcement. National Bank of Greece S.A. disclaims any obligation to update any forward-looking statements contained in this announcement, except as required pursuant to applicable law.

3

The following exhibits have been disclosed as a part of this Form 6-K:

4

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

5

Exhibit 99.1

Exhibit 99.2

GOVERNMENT GAZETTE

OF THE HELLENIC REPUBLIC

5 December 2015

Cabinet Act

No. 44 dated 05.12.2015

Amendment to the Cabinet Act No. 11/11.04.2014 on the “Provisions on issues pursuant to paragraph 11 of article 6A of Greek law 3864/2010 (Government Gazette, Issue A’ 119), as added by virtue of subparagraph A3 of paragraph A of article 2 of Greek law 4254/2014 (Government Gazette, Issue A’ 85)” (Government Gazette, Issue A’ 90).

THE CABINET

Taking into account:

1) The provisions of:

(a) article 82 paragraph 2 of the Greek Constitution;

(b) paragraphs 6, 11 and 12 of article 6A of Greek law 3864/2010 on the “Establishment of the Hellenic Financial Stability Fund” (Government Gazette, Issue A’ 119), as amended pursuant to article 1 of Greek law 4340/2015 on “The recapitalization framework of credit institutions and other provisions of the Ministry of Finance” (Government Gazette, Issue A’ 134) and in force;

(c) Cabinet Act No. 11/11.04.2014 on the “Provisions on issues pursuant to paragraph 11 of article 6A of Greek law 3864/2010 (Government Gazette, Issue A’ 119), as added by virtue of subparagraph A3 of paragraph A of article 2 of Greek law 4254/2014 (Government Gazette, Issue A’ 85)” (Government Gazette, Issue A’ 90);

(d) article 90 of the Codified Legislation on the Government and the Governmental Bodies (Presidential Decree no. 63/2005, Government Gazette, Issue A’ 98).

2) The fact that, pursuant to paragraph 6 of article 6A of Greek law 3864/2010, the measures referred to in paragraphs 1 to 4 of article 6A constitute reorganization measures, as defined in article 2 of the 2001/24/EC Directive of the European Parliament and Council dated 4 April 2001 on the reorganization and winding up of credit institutions, which has been transposed into Greek law by Greek law 3458/2006 on “The reorganization and winding up of credit institutions and other provisions” (Government Gazette, Issue A’ 94).

3) The fact that, in order for the financial burden of the rescue of a credit institution, which is considered to be viable by the competent authority, not to be solely and in principle borne by the tax payers, and that before granting to a bank any form of state aid, either for recapitalization purposes or as a measure of support of impaired assets, the bank itself must have exhausted any possible measure to strengthen its equity.

4) The necessity to amend Cabinet Act No. 11/11.04.2014, in order to be in compliance with the provisions of article 6A of Greek law 3864/2010, as amended by virtue of Greek law 4340/2015 and Greek law 4346/2015 on “Urgent measures on the implementation of the Fiscal Targets and Structural Reforms Agreement and other provisions” (Government Gazette, Issue A’ 152) and in force.

5) The proposal of the Minister of Finance.

6) The fact that no financial burden is caused to the State’s budget in relation to the issuance of this Act;

Hereby decides:

Cabinet Act No. 11/11.04.2014 on the “Provisions on issues pursuant to paragraph 11 of article 6A of Greek law 3864/2010 (Government Gazette, Issue A’ 119), as added by virtue of subparagraph A3 of paragraph A of article 2 of Greek law 4254/2014 (Government Gazette, Issue A’ 85)” (Government Gazette, Issue A’ 90) is replaced, as follows:

Article 1

1.              Prior to its recommendation to the Cabinet in order for the latter to take the measures set out in article 6A of Greek law 3864/2010, the Bank of Greece may appoint, pursuant to paragraph 4 of article 6A of Greek law 3864/2010, a valuer, who shall be independent from any public authority, and assign to him the valuation of the assets and liabilities of the credit institution in a reasonable and realistic manner. Such valuer cannot be the existing statutory auditor of the credit institution in question or have any other status entailing conflict of interests that could affect his independence. If another independent valuation of the credit institution in question is already ongoing by an independent auditor who has been appointed by the Bank of Greece for another reason, the latter’s valuation may be used for the purposes of the aforementioned valuation of paragraph 4 of article 6A of Greek law 3864/2010. Such valuation is incorporated in the recommendation of the Bank of Greece to the Cabinet.

2.              In case that the abovementioned valuation by the independent valuer cannot be performed in time, such valuation is conducted by the Bank of Greece based on a conservative approach.

3.              The valuation is taken into account in order to determine the need and the extent of application of the measures provided for in paragraph 2 of article 6A of Greek law 3864/2010.

4.              The valuation does not take into account any state capital support that will be granted following the publication of the Cabinet Act provided for in article 6A of Greek law 3864/2010 onwards.

Article 2

1.              The capital instruments and liabilities that are subject to conversion pursuant to article 6A of Greek law 3864/2010, are converted into common shares of the credit institution in question, at the amount resulting from the valuation provided for by article 1 divided by the offer price of the new common shares, as referred to under paragraph 3 and rounded down to the nearest whole number of shares.

2.              No amount shall be paid in cash for the fractions of common shares arising from the aforementioned calculation (before rounding down).

3.              The offer price of the common share is based on the value to which the implementation of paragraph 5 of article 7 of Greek law 3864/2010 in the context of the share capital increase process of the credit institution has resulted.

Article 3

1.         If the applicable measure is the decrease of the nominal value of the shares, such decrease is effected pursuant to the provisions of Greek codified law 2190/1920, in conjunction with the share capital increase that is resolved by the general meeting of shareholders of the credit institution.

2.         If the applicable measure is the decrease of the nominal value of the subordinated liabilities or the unsecured senior liabilities non-preferred by mandatory provisions of law, such decrease is considered to have taken place upon issuance of the Cabinet Act provided for by paragraph 1 of article 6A of Greek law 3864/2010.

3.         In the event of conversion, such conversion takes place simultaneously with the publication of the aforementioned Cabinet Act and the new common shares to be issued are allocated to the beneficiaries in the manner provided for by article 2 of this Cabinet Act.

4.         For the proper delivery of such shares to their owners, the credit institution informs the beneficiaries about the completion of the conversion and the actions to which they must proceed in order to receive their shares.

Article 4

For the purposes of the conversion or write down, as the case may be, of the liabilities falling within the scope of paragraphs 1 and 3 of article 6A of Greek law 3864/2010, the recommendation by the Bank of Greece and the Cabinet Act provided for in paragraph 1 of article 6A of Greek law 3864/2010, include a detailed list of the abovementioned liabilities and determine their submission to the measures provided for by article 6A of Greek law 3864/2010.

Article 5

1.         For the valuation conducted in accordance with paragraph 9 of article 6A of Greek law 3864/2010, the Bank of Greece shall appoint a valuer who is independent from any public authority, including the Ministry of Finance and the Bank of Greece, in order to ensure the performance of a fair and objective valuation of the assets and liabilities of the credit institution.

2.         The valuation provided for in paragraph 9 of article 6A of Greek law 3864/2010 reflects:

a)                                      The treatment that the capital instruments and liabilities falling within the scope of paragraphs 1 and 3 of article 6A of Greek law 3864/2010 would have should the credit institution was placed under special liquidation immediately before the issuance of the Cabinet Act provided for by paragraph 1 of article 6A of Greek law 3864/2010.

b)                                      The treatment of the abovementioned capital instruments and liabilities on the basis of the Cabinet Act provided for by paragraph 1 of article 6A of Greek law 3864/2010.

c)                                       Whether there is any differentiation between items (a) and (b) above.

3.         The said valuation:

a)                                      is based on the assumption that the credit institution would be placed under special liquidation proceedings immediately before the issuance of the Cabinet Act provided for by paragraph 1 of article 6A of Greek law 3864/2010;

b)                                      is based on the assumption that the abovementioned Cabinet Act would not have been issued;

c)                                       does not take into consideration any state capital support or emergency liquidity assistance provided to the credit institution.

Article 6

In case that, following the application of the measures of the Cabinet Act provided for by paragraph 1 of article 6A of Greek law 3864/2010, the holders of the capital instruments and liabilities that are subject to the measures of article 6A of the same law, prove that they are entitled to compensation, pursuant to paragraph 8 of the same article, the Greek State, following the payment of any such compensation, has the right to seek the compensation that has been paid from the banking system.

This Act shall be published on the Government Gazette.

THE PRIME MINISTER

THE CABINET MEMBERS

Exact Copy

The General Secretary of the Government

MICHAEL KALOGIROU

Exhibit 99.3

Exhibit 99.4

GOVERNMENT GAZETTE

OF THE HELLENIC REPUBLIC

7 December 2015

Cabinet Act

No. 45 dated 05.12.2015

Implementation of measures provided for in article 6A of Greek law 3864/2010 (Government Gazette Issue A’ 119), prior to the provision of capital support by the Hellenic Financial Stability Fund to the credit institution under the name “National Bank of Greece S.A.”.

THE CABINET

Taking into account:

1) The provisions of:

(a) article 82 paragraph 2 of the Greek Constitution;

(b) paragraphs 1, 6, 8, 9, 10 and 12 of article 6A of Greek law 3864/2010 on the “Establishment of the Hellenic Financial Stability Fund” (Government Gazette, Issue A’ 119), as amended pursuant to article 1 of Greek law 4340/2015 on “The recapitalization framework of credit institutions and other provisions of the Ministry of Finance” (Government Gazette, Issue A’ 134) and in force;

(c) the Cabinet Act No. 11/11.04.2014 on the “Provisions on issues pursuant to paragraph 11 of article 6A of Greek law 3864/2010 (Government Gazette, Issue A’ 119), as added by virtue of subparagraph A3 of paragraph A of article 2 of Greek law 4254/2014 (Government Gazette, Issue A’ 85)”, as amended by Cabinet Act No. 44/05.12.2015 [Amendment to the Cabinet Act No. 11/11.04.2014 on the “Regulation of issues pursuant to paragraph 11 of article 6A of Greek law 3864/2010 (Government Gazette, Issue A’ 119), as added by virtue of subparagraph A3 of paragraph A of article 2 of Greek law 4254/2014 (Government Gazette, Issue A’ 85)” (Government Gazette, Issue A’ 90)] (Government Gazette Issue A’ 165) ;

(d) article 90 of the Codified Legislation on the Government and the Governmental Bodies (Presidential Decree no. 63/2005, Government Gazette, Issue A’ 98).

2) The fact that, the measures provided for in paragraph 2 of article 6A of Greek law 3864/2010 constitute reorganization measures, as defined in article 2 of the 2001/24/EC Directive of the European Parliament and Council dated 4 April 2001 on the reorganization and winding up of credit institutions, which has been transposed into

Greek law by Greek law 3458/2006 on “The reorganization and winding up of credit institutions and other provisions” (Government Gazette, Issue A’ 94).

3) The fact that, in order for the financial burden of the rescue of a credit institution, which is considered to be viable by the competent authority, not to be solely and in principle borne by the tax payers, and that before granting to a bank any form of state aid, either for recapitalization purposes or as a measure of support of impaired assets, the bank itself must have exhausted any possible measure to strengthen its equity, aiming, by this, to the minimum possible burden of the public debt.

4) The fact that the measures provided for in article 6A of Greek law 3864/2010 aim to the protection of the public interest, constitute provisions of binding and immediate effect and prevail over any contrary provision.

5) The recommendation of the Bank of Greece, according to the Decision No. 165/1/05.12.2015 of the Credit and Insurance Committee of the Bank of Greece regarding the implementation of the measures provided for in article 6A of Greek law 3864/2010, prior to the grant of capital support by the Hellenic Financial Stability Fund to the credit institution under the name “National Bank of Greece S.A.”, and the justification referred thereof.

6) The fact that due to the application of the present act, the public resources are protected while the provision of state aid to National Bank of Greece S.A. by the Hellenic Financial Stability Fund is minimized and as a result the minimum possible burden of the public debt is satisfied.

7) The fact that no financial burden is caused to the State’s budget in relation to the issuance of this Act;

Hereby decides:

1. The mandatory implementation of measures described in paragraph 2 of article 6A of Greek law 3864/2010, as in force, regarding the allocation of the remaining capital shortfall to the holders of capital instruments or other liabilities of the credit institution under the name National Bank of Greece S.A.

2. The instruments or the liabilities of the credit institution named National Bank of Greece S.A. that are subjected to the measures described in article 6A of Greek law 3864/2010 are determined by class, type, rate and amount of participation, as follows:

It shall be noted that in cases iii — vii, the guarantee of the credit institution together with the callable subordinated debt securities issued by the credit institution under ISIN XS0171836561, XS0204339575, XS0204339146, XS0212896632, XS0274178507 to the extent that they are not own-held, it is suggested to be converted, as described in the table above, into common shares of the credit institution in accordance with paragraph

2 case (c) and paragraph 3 of article 6A of Greek law 3864/2010, and such shares shall be given to the holders of securities issued by NBG Funding Limited, in favor of whom the guarantee was granted.

As of, and by, the conversion, the liabilities of the credit institution deriving both from the guarantee and the callable subordinated debt securities issued by the credit institution under ISIN XS0171836561, XS0204339575, XS0204339146, XS0212896632, XS0274178507, which only serve the funding for the purpose of fulfilling the liabilities of NBG Funding Limited against its creditors, cease entirely to be in force.

3. A summary of the present act shall be published on the Official Journal of the European Union, in the Greek language, and in two daily newspapers circulating throughout the whole territory of the following member states, in their corresponding official languages: Bulgaria, United Kingdom, Cyprus, Malta, Romania including the content as described for in paragraph 10 of article 6A of Greek law 3864/2010.

This Act shall be published on the Government Gazette.

THE PRIME MINISTER

THE CABINET MEMBERS

Exact Copy

The General Secretary of the Government

MICHAEL KALOGIROU