The Prostate Cancer Prevention Trial is the first phase III (randomized, placebo-controlled, prospective) population-based study to determine whether the risk of prostate cancer can be reduced. Between 1994 and 1997, 18,882 men were randomized to either finasteride or placebo at 219 sites in the United States. The study design included annual digital rectal examination and PSA determinations with PSA performed centrally with reports provided to sites corrected for treatment arm (as finasteride lowers PSA level). Because of a number of potential biases that could confound disease ascertainment all patients were scheduled for an end-of-study prostate biopsy. End-of-study prostate biopsies began in 2000, and the final biopsy is expected in 2004, with results of the study anticipated shortly thereafter. The high participant interest and extensive data collected for this study demonstrate the extraordinary opportunity for chemoprevention trials of prostate cancer in the United States