A systematic search for polyps was carried out in 1,499 autopsy specimens of large intestine from Cali, Colombia, a low-incidence area for colo-rectal carcinoma. No cases of carcinoma were found in the series studied. The prevalence of each of the main types of polyps, namely adenomatous, hyperplastic and retention, is described. Retention polyps tend to disappear with age. Hyperplastic polyps appear around the 4th decade of life, are often multiple, are mostly found in the sigmoid and rectum and their prevalence does not increase appreciably with age; these findings are interpreted as added evidence against an association between hyperplastic polyps and carcinoma of the colon and rectum. Adenomatous polyps increase in prevalence with age and are more often multiple and in males tend to be concentrated in the sigmoid; tentative comparisons of Cali data with findings from countries at high risk for colo-rectal cancer suggest a statistical association between prevalence of adenomas and incidence of carcinoma of the colon and an even stronger association between colon cancer and atypical cellular changes in adenomas. It is suggested that populations at high risk to colon cancer are probably characterized by an increased prevalence of adenomatous polyps, particularly in the sigmoid colon of males, and display a larger proportion of multiple polyps and atypical cellular changes.