OSI Pharmaceuticals, Inc.
41 Pinelawn Road
Melville, NY 11757
T 631.962.2000 F 631 752.3880
www.osip.com

                             July 22, 2009

Via Federal Express and EDGAR

U.S. Securities and Exchange Commission
Division of Corporation Finance
100 F Street, N.E.
Washington, D.C. 20549

Attn: Ms. Laura Crotty, Staff Attorney

Re:  OSI Pharmaceuticals, Inc. (“OSI”)
Form 10-K for the Fiscal Year ended December 31, 2008
Definitive Proxy Statement
Filed April 29, 2009
File No. 000-15190

Dear Ms. Crotty:

     This letter is in response to your letter dated July 20, 2009 relating to OSI’s Form 10-K for the fiscal year ended December 31, 2008, filed on February 27, 2009, and Definitive Proxy Statement, filed on April 29, 2009 (File No. 000-15190). Pursuant to our conversation on July 21, 2009, OSI is requesting an extension of the ten (10) business day response date in your letter to ensure that its management has the opportunity to fully consider and respond to your comments. OSI proposes to provide a response to your letter on or before August 21, 2009, which it will file with the Securities and Exchange Commission (the “SEC”) via hard copy to you and EDGAR.

     OSI has filed this correspondence today with the SEC via EDGAR. If you have any questions concerning the foregoing, please do not hesitate to contact me at (631) 962-2048.

Sincerely,

 

/s/  Jon Brooks

Jon Brooks 
Associate General Counsel — Corporate and Securities 

cc:  Barbara A. Wood, Esq., Senior Vice President,
General Counsel and Secretary