Although early detection and treatment of prostate cancer is widely advocated, this so-called secondary prevention approach has a number of drawbacks. First, it is not yet certain that active treatment of localized prostate cancer offers any advantage over surveillance. Second, screening may detect indolent tumors while missing some virulent ones. Third, treatment is not uniformly successful, even in patients with early disease. Fourth, radical prostatectomy and radiotherapy are associated with considerable side effects. And finally, the economic and psychological costs of large-scale screening cannot be overlooked. Although attention has been focused on the possibility of primary prevention, neither large-scale dietary manipulation nor long-term prophylactic use of retinoids is considered feasible. With the recent approval of the 5-alpha-reductase inhibitor finasteride for the treatment of benign prostatic hyperplasia, the opportunity for primary chemoprevention has moved closer to reality. The Prostate Cancer Prevention Trial (PCPT), a randomized, placebo-controlled study expected to enroll 18,000 healthy men over the age of 55, is currently addressing the question of whether finasteride prophylaxis can reduce the incidence of prostate cancer over a 7-year period. This is a US government work. There are no restrictions on its use.