M. E. Brown and J. L. Margot, California Institute of Technology, report the discovery of a satellite to (87) Sylvia.  The projected separation between primary and secondary was 0.59'' in H-band images obtained on 2001 Feb 18.5 UT using the adaptive optics system on the 10-m W. M. Keck II telescope on Mauna Kea.  Little relative motion was apparent in images obtained an hour apart (upper limit 0.02'').  The brightness ratio was measured to be 420+/-70, implying a ~1:20 ratio of sizes.