Although the incidence of most human malignancies including cancer of the gastrointestinal tract increases dramatically with advancing age, the precise role of aging in that increase remains a matter of continued controversy. Many probable explanations for the age-related rise in cancer incidence have been offered including altered carcinogen metabolism and the cumulative effects of protracted exposure to cancer-causing agents. Neoplasia of the stomach or colon is a multi-stage process with hyperproliferation being central to the initiation of carcinogenesis. Since aging is associated with increased gastrointestinal mucosal cell proliferation, the possibility that aging itself may render target cells more susceptible to carcinogenic transformation continues to be an area of intense interest and study. This review will examine the evidence for age-related alterations in the structural and functional properties of the gastric and colonic mucosa in an effort to further elucidate the potential mechanisms of carcinogenesis which may be involved during the aging process.