A world-wide comparative study of the frequency and characteristics of latent carcinoma of the prostate was undertaken in seven areas, using standardized methods and “blind” microscopic evaluation in order to reduce selection and observer bias. The morphological features of 350 latent carcinomas found in 1,327 prostates were examined. Two Chinese populations, from Hong Kong and Singapore, showed a low frequency of latent carcinoma in comparison with western Europeans in Sweden and the Federal Republic of Germany and negroes from Jamaica; an intermediate position was found for Israelis and black Ugandans. The frequency of small latent carcinomas was about 12% in all the areas investigated and did not vary with age. Rates for larger latent carcinomas increased sharply with age and showed an area-to-area variation resembling that of clinical carcinoma of prostate. The small carcinomas were almost exclusively situated in the outer half of the prostate and latent carcinomas of all sizes were evenly distributed between the anterior and posterior halves of the prostate and the right and left sides of the outer prostatic shell. Certain disagreements in diagnosis were noted when the sections from each area were evaluated independently by a different pathologist. Most of these disagreements were resolved by re-reading the sections; their occurrence had no significant effect on the geographical comparisons.