In recent years, there have been major advances regarding the understanding of the pathogenesis of sporadic and hereditary colorectal cancer on the basis of molecular research. The clinical implications of this knowledge differ for the sporadic and hereditary forms. In sporadic colorectal cancer, gene mutations occur in colorectal cells but not as germline mutations. Even though molecular data currently do not influence the clinical management of this form of colorectal cancer, promising molecular approaches exist for the assessment of prognosis, early detection, prevention, and therapy. Germline mutations are the cause of hereditary colorectal cancers, in which molecular methods have a major impact on diagnosis and therapy. Prophylactic surgery is accepted for patients with familial adenomatous polyposis (FAP), but not for patients with hereditary non-polyposis colorectal cancer (HNPCC), the second main form of hereditary colorectal cancer. Further studies will have to clarity this issue.