Sporadic cancer develops approximately at 65 years of age. Epidemiologic data suggest that dietary factors probably are the most influential in colorectal carcinogenesis. In contrast, individuals who have relatives with colorectal neoplasia have an increased risk of these tumors themselves, which will appear earlier in life. The actual incidence of hereditary colorectal cancer is unknown. However, the incidence is much higher compared with well-known hereditary colorectal diseases, such as familial adenomatous polyposis.An overview of the recent progress in the field of both clinical and basic research on hereditary colorectal cancer must be made.Twenty-two family pedigrees were analyzed at Hamamatsu University School of Medicine, including the largest family pedigree in Japan, which contained 24 cases of colorectal cancer occurring over five generations. In 1995, when the International Symposium on Hereditary Cancer was held in Hamamatsu, 4,109 family pedigrees were investigated and analyzed, including 394 cases in 109 family pedigrees that met the Amsterdam Minimum Criteria. Information was collected by sending questionnaires to major hospitals in Japan. Basic updated data presented at the eighth and ninth International Collaborative Group on Hereditary Colorectal Cancer were also quoted.Because of the discovery of mismatch repair genes as that responsible for hereditary nonpolyposis colorectal cancer, modification of the Amsterdam Criteria is necessary. Replication error, as a mutator phenotype of mismatch repair genes, is a useful predictor of second primary malignancies. Surveillance or prophylactic surgery is still a controversial issue.