ICLR ICON PLC

EXPLANATORY NOTE

This Post-Effective Amendment No. 1 (“Post-Effective Amendment No. 1”) relates to the Registration Statement on Form S-8 (File No. 333-152802) (the “Registration Statement”) of ICON plc (the “Registrant”), which was filed with the Securities and Exchange Commission on August 6, 2008.  The Registration Statement registered a total of 6,500,000 of the Registrant’s Ordinary Shares, par value 6 euro cents each (“Shares”), consisting of 3,000,000 Shares reserved for issuance under  the ICON plc Employee Share Option Plan 2003 (the “2003 Employee Plan”), 200,000 Shares under the ICON plc Consultants Share Option Plan 2008 (the “2008 Consultants Plan”), 2,800,000 Shares under the ICON plc Employees Share Option Plan 2008 (the “2008 Employee Plan”) and 500,000 Shares under the ICON plc 2008 Employee Restricted Share Unit Plan (the “2008 RSU Plan”) (provided that any Shares available for issuance but not issued under the 2008 Consultants Plan were available for issuance under the 2008 Employee Plan).  The Registration Statement also registered such additional Shares as may be issued in the event of a share dividend, recapitalization, share split, reverse split, reorganization, merger, amalgamation, consolidation or other similar dilutive event. After giving effect to a 2-for-1stock split by issuance of bonus Shares to holders of record on August 8, 2008, there were registered under the Registration Statement 6,000,000 Shares under the 2003 Employee Plan, 400,000 Shares under the 2008 Consultants Plan, 5,600,000 Shares under the 2008 Employee Plan and 1,000,000 Shares under the RSU Plan (provided that any Shares available but not issued under the 2008 Consultants Plan were issuable under the 2008 Employee Plan).

On February 14, 2017, the Board of Directors of the Registrant amended and restated the 2008 Consultants Plan and 2008 Employee Plan.  Prior to the amendments, the total number of Shares available for issuance under the 2008 Consultants Plan was 400,000 Shares, and the total number of shares available for issuance under the 2008 Employee Plan was 6,000,000 Shares, provided that the number of Shares available under the 2008 Employee Plan was reduced by the number of Shares issued or to be issued under options granted under the 2008 Consultants Plan.  Pursuant to the amendments, the total number of Shares available for issuance under the 2008 Consultants Plan was increased from 400,000 Shares to 1,000,000 Shares, and the number of Shares by which Shares available under the 2008 Employee Plan may be reduced also was increased from 400,000 Shares to 1,000,000 Shares.  In addition, the term of each plan was extended until February 14, 2027.  As a result of the amendments, the Registrant is filing this Post-Effective Amendment No. 1 to file as exhibits the 2008 Consultants Plan and 2008 Employee Plan (each as amendment and restated effective as of February 14, 2017) and to reflect that the number of Shares available for issuance under the 2008 Consultants Plan was increased from 400,000 to 1,000,000 Shares and the Shares available under the 2008 Employee Plan may be reduced by the same amount, provided that Shares available for issuance that are not issued under the 2008 Consultants Plan will be available for issuance under the 2008 Employee Plan.  No additional Shares are being registered by this Post-Effective Amendment No. 1.