Statement of Changes in Beneficial Ownership (4)

FORM 4 [ X ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response... 0.5
	Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

1. Name and Address of Reporting Person ^* Flynn James E	2. Issuer Name and Ticker or Trading Symbol RHYTHM PHARMACEUTICALS, INC. [ RYTM ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __ X __ 10% Owner _____ Officer (give title below) __ X __ Other (specify below) Possible Member of 10% Group
(Last) (First) (Middle) 780 THIRD AVENUE, 37TH FLOOR,	3. Date of Earliest Transaction (MM/DD/YYYY) 10/10/2017
(Street) NEW YORK, NY 10017 (City) (State) (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _ X _ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. Code (Instr. 8)		4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	10/10/2017		C		291005	A	⁽¹⁾	291005	I	Through Deerfield Private Design Fund III, L.P. ⁽²⁾ ⁽³⁾
Common Stock	10/10/2017		C		291005	A	⁽¹⁾	291005	I	Through Deerfield Special Situations Fund, L.P. ⁽²⁾ ⁽³⁾
Common Stock	10/10/2017		P		177500	A	$17.00	468505	I	Through Deerfield Private Design Fund III, L.P. ⁽²⁾ ⁽³⁾
Common Stock	10/10/2017		P		177500	A	$17.00	468505	I	Through Deerfield Special Situations Fund, L.P. ⁽²⁾ ⁽³⁾

*Table II - Derivative Securities Beneficially Owned ( e.g.* , puts, calls, warrants, options, convertible securities)**
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)			11. Nature of Indirect Beneficial Ownership (Instr. 4)
Series A Preferred Stock	⁽¹⁾	10/10/2017		C			2668518	⁽¹⁾	⁽¹⁾	Common Stock	291005	⁽¹⁾	0	I	Through Deerfield Private Design Fund III, L.P. ⁽²⁾ ⁽³⁾
Series A Preferred Stock	⁽¹⁾	10/10/2017		C			2668518	⁽¹⁾	⁽¹⁾	Common Stock	291005	⁽¹⁾	0	I	Through Deerfield Special Situations Fund, L.P. ⁽²⁾ ⁽³⁾

Explanation of Responses:
(1)	Each share of Series A Preferred Stock automatically converted into 0.1090513 shares of the Issuer's common stock upon the closing of the Issuer's initial public offering (on an adjusted basis, after giving effect to the 1-for-9.17 reverse stock split effected by the Issuer in connection with its initial public offering).
(2)	This Form 4 is being filed by the undersigned as well as the entities listed on the Joint Filer Information Statement attached as an exhibit hereto (the "Reporting Persons"). Deerfield Mgmt III, L.P. is the general partner of Deerfield Private Design Fund III, L.P. ("Fund III"). Deerfield Mgmt, L.P. is the general partner of Deerfield Special Situations Fund, L.P. (collectively with Fund III, the "Funds"). Deerfield Management Company, L.P. is the investment manager of the Funds. James E. Flynn is the sole member of the general partner of each of Deerfield Mgmt III, L.P., Deerfield Mgmt, L.P. and Deerfield Management Company, L.P.
(3)	In accordance with Instruction 4 (b)(iv) to Form 4, the entire amount of the Issuer's securities held by the Funds is reported herein. For purposes of Section 16 of the Securities Exchange Act of 1934, as amended, each Reporting Person disclaims beneficial ownership of any such securities, except to the extent of his/its indirect pecuniary interest therein, if any, and this report shall not be deemed an admission that such Reporting Person is the beneficial owner of such securities for purposes of Section 16 or otherwise.

Remarks:
Jonathan Isler, Attorney-in-Fact: Power of Attorney, which is hereby incorporated by reference to Exhibit 24 to a Form 3 with regard to Proteon Therapeutics, Inc. filed with the Securities and Exchange Commission on August 4, 2017 by Deerfield Special Situations Fund, L.P., Deerfield Partners, L.P., Deerfield International Master Fund, L.P., Deerfield Private Design Fund III, L.P., Deerfield Private Design Fund IV, L.P., Deerfield Mgmt, L.P., Deerfield Mgmt III, L.P., Deerfield Mgmt IV, L.P., Deerfield Management Company, L.P., and James E. Flynn.

Reporting Owners
Reporting Owner Name / Address	Relationships
Reporting Owner Name / Address	Director	10% Owner	Officer	Other
Flynn James E 780 THIRD AVENUE, 37TH FLOOR NEW YORK, NY 10017		X		Possible Member of 10% Group
Deerfield Mgmt L.P. 780 THIRD AVENUE 37TH FLOOR NEW YORK, NY 10017		X		Possible Member of 10% Group
DEERFIELD MANAGEMENT CO 780 THIRD AVENUE, 37TH FLOOR NEW YORK, NY 10017		X		Possible Member of 10% Group
Deerfield Special Situations Fund, L.P. 780 3RD AVENUE 37TH FLOOR NEW YORK, NY 10017		X		Possible Member of 10% Group
Deerfield Mgmt III, L.P. 780 THIRD AVENUE, 37TH FLOOR NEW YORK, NY 10017		X		Possible Member of 10% Group
Deerfield Private Design Fund III, L.P. 780 THIRD AVENUE, 37TH FLOOR NEW YORK, NY 10017		X		Possible Member of 10% Group

Signatures
/s/ Jonathan Isler, Attorney-in-Fact		10/10/2017
^** Signature of Reporting Person		Date

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
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