Prostate cancer is a significant cause of disease and death, making it an attractive target for chemoprevention. The association between lifetime exposure to dihydrotestosterone and risk of developing prostate cancer suggests that chemoprevention is possible with 5α-reductase inhibition. The recently completed Prostate Cancer Prevention Trial indicates that chemoprevention is possible with the 5α-reductase inhibitor finasteride. Development of a cost-effective chemoprevention strategy for prostate cancer is evolving, and is expected to have significant positive economic and public health benefits.