Prostate cancer is an appropriate target for primary chemoprevention because of its ubiquity, disease-related mortality, treatment-related morbidity, and long latency period. The PCPT and REDUCE trials demonstrate that this cancer can be prevented by a relatively nontoxic oral pharmacologic agent (5alpha-reductase inhibitors). Evidence from the SELECT trial argues against the recommendation of the use of vitamins and micronutrients as chemoprevention of prostate cancer. Dietary modification may substantially alter a man's risk of prostate cancer, but the specific dietary manipulations that are necessary are poorly defined and these may need to be instituted in early adulthood to be successful. 5alpha-reductase inhibitors represent an effective primary prevention strategy, and these agents should be used more liberally for the prevention of prostate cancer, particularly in high-risk patients.