In 1990, prostate cancer will be the most common cancer diagnosed in U.S. men and will be the second-leading cause of cancer mortality in these men. One in ten U.S. men will develop prostate cancer in his lifetime. Twenty thousand prostate cancer cases occur each year in men under the age of 65. The average number of years of life lost for a man dying of prostate cancer is nine. In addition, both incidence and mortality of prostate cancer are increasing. A review of the literature regarding prostate cancer is timely in light of recent studies examining possible predisposing factors for this disease. In this review, a framework for understanding genetic and environmental factors which may predispose to prostate cancer is presented. The identification of factors which predispose to clinical prostate cancer offers the possibility of lowering the incidence and mortality of prostate cancer in the United States. Epidemiologic evidence regarding possible predisposing factors to prostate cancer is reviewed.