A sample of approximately 400 B^0_d/B-bar^0_d -> J/psi K^0_s
decays collected in pbar p collisions by the CDF detector is used to directly
measure the CP-violation parameter sin(2B).  We find sin(2B) =
0.79^0.41_-0.44, favoring the standard model expectation of a large CP
violation in this B^0 decay mode.