Osi Pharmaceuticals (OSIP) 10-Q 2008 Q1 Quarterly report

EXHIBIT 32.1

OSI PHARMACEUTICALS, INC.

CERTIFICATION PURSUANT TO
18 U.S.C. § 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of OSI Pharmaceuticals, Inc. (the “Company”) on Form 10-Q for the quarter ended March 31, 2008 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Colin Goddard, Ph.D., Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. § 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and result of operations of the Company.

Date: May 8, 2008

/s/ Colin Goddard, Ph.D.  

Colin Goddard, Ph.D. 

Chief Executive Officer 

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