LIMITED POWER OF ATTORNEY


	KNOW ALL MEN BY THESE PRESENTS, that
the undersigned hereby constitutes and appoints Robert L. Van Nostrand the
undersigned's true and lawful attorney-in-fact and agent, with full power
of substitution and re-substitution, for the undersigned and in the
undersigned's name, place and stead, to execute and file with the
appropriate offices on the undersigned's behalf all Forms 3, 4 and 5 under
Section 16 of the Securtities Exchange Act of 1934, as amended, with
respect to the undersigned's transactions in, and ownership of, the
securities of OSI Pharmaceuticals, Inc., a Delaware corporation, granting
unto said attorney-in-fact and agent full power and authority to do and
perform each and every act deemed requisite and necessary to be done in
order to carry out the foregoing as fully and to all intents and purposes
as the undersigned might and could do in person, hereby ratifying and
confirming all that said attorney-in-fact and agent or his substitute or
substitutes may lawfully do or cause to be done by virtue hereof.

	IN
WITNESS WHEREOF, the undersigned has executed this Power of Attorney as of
the 2nd day of May, 2005.






Katharine B. Stevenson
						Signature




Katharine B. Stevenson
						Print Name