BACKGROUND: A variety of innovative approaches to the prevention of prostate cancer are now available, including selenium, alpha tocopherol, dietary interventions, and vitamin D. Perhaps the most promising opportunity is based upon considerable evidence that cumulative androgen exposure of the prostate contributes to the age-related risk of prostate cancer. METHODS: The Prostate Cancer Prevention Trial has completed randomization of over 18,000 healthy men to either finasteride or placebo. CONCLUSIONS: While the primary objective of this study is to determine whether finasteride can reduce the period prevalence of prostate cancer over a 7-year period, the biologic and data resources of this study will provide multiple opportunities to better understand this most common cancer in U.S. men.