The prevalences of bowel diseases (hemorrhoids, appendicitis, polyps, ulcerative colitis, irritable bowel syndrome, diverticular disease, and colon cancer) are similar in South African whites and in populations of prosperous western countries. Among rural South African blacks with a traditional life style, these diseases are very uncommon or almost unknown. Among the urban South African blacks with a partially westernized life style, the diseases remain uncommon. Frequencies of appendectomies and colon cancer in urban blacks have increased little during the last three decades, although an increase undoubtedly has occurred in the frequency of diverticular disease. Frequencies of bowel diseases in South African Indian and colored (Eurafrican, Malay) populations are intermediate. Because the diseases are almost entirely of environmental causation (due to principally to changes in diet), prevalences almost certainly will increase in blacks, Indians and coloreds, as their way of life becomes further westernized.