For men who have hormone-refractory prostate cancer, current treatment options are somewhat limited, with docetaxel the only agent showing a significant prolongation of survival. Several groups have investigated therapeutic approaches involving stimulation of an immune response against progressive prostate cancer. Several features of prostate cancer suggest that it may be a good target for immunotherapy. Constant pressure by the immune system forces tumors to evolve multiple ways to escape immune assault, however, and it is thus unlikely that single-agent immunotherapy for prostate cancer will achieve maximal clinical benefit. Most likely, successful immunotherapy will eventually require either the combination of multiple immunologic approaches or the combination of immunologic approaches with conventional therapy.