Prostate cancer is a leading cause of cancer morbidity and mortality in the United States. Animal and clinical studies performed four decades ago suggested that immunological approaches might be useful for the treatment of prostate cancer. The wealth of information that has been learned over the last two decades has suggested many new directions to the immune-based therapy of prostate cancer, including passive and active immunotherapy approaches. The findings from current trials, and the likely combination of current immunotherapy approaches with conventional therapies, portends a hopeful future for the treatment of prostate cancer.