Progress has continued in explicating the genetics of inherited predispositions to colorectal cancer and the molecular events that lead to tumorigenesis. New polymorphic DNA markers have been described for the presymptomatic diagnosis of familial adenomatous polyposis and a candidate gene has been characterized. Pedigree studies have suggested that there may be an inherited predisposition to many apparently nonfamilial colorectal cancers and a genetic model of tumorigenesis in common colorectal cancer has been proposed that includes the activation of dominantly acting oncogenes and the inactivation of growth suppressor genes. Two features of colorectal cancer make it a particularly good model for studying neoplasia. There are several well-defined rare inherited syndromes that predispose to the development of colorectal cancer in an autosomal dominant manner, and the majority of carcinomas are thought to arise from preexisting benign adenomatous polyps, allowing the analysis of genetic changes during tumorigenesis.