OBJECTIVE Colorectal malignancies are less common in developing than developed nations because of lower per capita income and higher dietary fiber consumption. This clinicopathologic study attempts to determine changes in the pattern of these neoplasms in Ibadan, Nigeria, during the last two decades. METHODS The present study is based on the clinical Cancer Registry records and gross and morphologic surgical pathology findings of 526 patients with histologically verified malignant colorectal neoplasms received in the Department of Pathology, University College Hospital, Ibadan, between 1971 and 1990. RESULTS Colonic malignancies increased by 81 percent, whereas rectal malignancies decreased 16.1 percent in frequency (P < 0.05). The modal ages were 55 to 60 years and 45 to 50 years for colonic and rectal neoplasms, respectively, in contrast to reported peak occurrence in the seventh decade among Caucasians. Colonic neoplasms were predominantly right-sided (34.3 percent cecal), abdominal mass and pain being major clinical manifestations. This differs from the pattern in American Negroes, among whom colonic carcinomas are predominantly left-sided, dyschezia being an important presentation. As in most other studies, adenocarcinomas were the predominant neoplasms. CONCLUSIONS Further work is required to determine prognostically significant features of colorectal cancer in our environment.