Prostates obtained at autopsy from black and white males in the United States of America, from Colombians, from Japanese migrants in Hawaii, and from Japanese in Japan (all over 50 years old) were serially step-sectioned and examined microscopically using identical techniques and diagnostic criteria. The age-adjusted overall prevalence of latent carcinoma was significantly higher in US blacks (36.9%), in US whites (34.6%) and in Colombians (31.5%) than in Japanese in Japan (20.5%). There was no significant difference in prevalence between Japanese migrants in Hawaii (25.6%) and Japanese in Japan. When the carcinomas were subdivided into latent infiltrative type (LIT) and latent non-infiltrative type (LNT), the LIT component reflected upon the overall prevalence of latent carcinoma. There was an increase in the overall prevalence of latent carcinoma and in the prevalence of LIT tumors with age in Japanese migrants to Hawaii and in Japanese of Japan but only a suggestive increase in blacks and whites in the United States. There was no significant relation between age and prevalence in Colombia. In LNT tumors, there was no consistent trend related to race or age. The size of LIT tumors was significantly greater than that of LNT tumors in all races or in each decade of total material. There were many large LIT tumors in blacks and whites in the United States. These results suggest that the prevalence of LIT tumors shows a race variation similar to the incidence of clinical carcinoma of the prostate, and that LNT tumors probably remain latent during the individual's life span.