Patients who were registered by the Japanese Society for Cancer of the Colon and Rectum between 1978 and 1983 were examined clinically and pathologically, in terms of colorectal cancer with familial accumulation. The incidence of patients with a family history of colorectal cancer (FH+ group)--patients with adenomatosis coli were excluded--was 6.5% in 15,369 colorectal cancer patients. The incidence of patients with a family history of malignant tumors other than colorectal cancer was 27.7%. Comparison of the FH+ group with the FH- group (patients without a family history of colorectal cancer) revealed the incidence of colonic cancer to be significantly higher than that of rectal cancer in the FH+ group (P < 0.01). The patients with colonic cancer in the FH+ group were significantly younger than those in the FH- group (P < 0.01), but there was no age-dependent difference between patients with rectal cancer in the two groups. There was no difference in sex ratio and there was little difference in the subsite of the primary lesion in the colon between the FH+ and FH- groups. The incidence of multiple primary colorectal cancer was significantly higher in patients with colonic cancer in the FH+ group than in the FH- group (P < 0.01). The incidence of multiple primary cancer in sites other than the colon and rectum was significantly higher in the FH+ group (P < 0.01), but no significant difference was found in the site of lesions. The prognosis of patients in the FH+ group was significantly better than that of those in the FH- group; however, there were no differences in background factors such as findings of the primary lesion, status of metastasis, clinical stage and rate of curative resection between the groups.