Familial occurrence in excess of that expected by chance is common among cases of colon cancer. Only a small fraction of these familial cases arise from well-described syndromes. There are epidemiologic, colonoscopic, genealogic data base and large prospective studies that characterize the familial occurrence and risk for common colon cancer. Kindred studies suggest that common familial occurrence arises from inherited susceptibility of a mild to moderate magnitude. The responsible genes are yet to be identified, though a number of candidate genes have been suggested. Clinical features, especially age at diagnosis and number of first-degree relatives with colon cancer, already allow stratification of familial risk. Risk stratification is important for colon cancer screening, as some higher-risk persons should probably have more intensive screening. Research is needed to identify the genes or their polymorphisms that give rise to common inherited susceptibility for colon cancer, to examine how susceptibility genes interact with environmental factors and give rise to colonic neoplasms and to verify suggested screening approaches that incorporate familial risk.