This study of the epidemiology of cancer of the prostate was based on a retrospective investigation of 300 patients with cancer of the prostate and 400 controls, a review of the charts of an additional 350 patient with prostate cancer, and a review of the literature. The main etiologic lead to which this study could not contribute is the rarity of clinical prostatic cancer in Japan and its increase among Japanese immigrants in the U.S. However, the low rate among Jewish males in the U.S. seems to be related to a lower rate of prostatic cancer among immigrants from Eastern Europe. U.S. Negroes have a higher incidence rate than Caucasians. No significant relationship was found to socioeconomic status, marital status, fertility, social habits, previous diseases, weight, height, hair distribution, or laboratory data.