Variation in prognosis between different colorectal cancer (CRC) patient groups was studied by comparing the survival rates of patients belonging to three cancer predisposition groups with those with sporadic CRC. The high-risk groups included 43 members of hereditary nonpolyposis colorectal cancer (HNPCC) families, 25 patients with familial adenomatous polyposis (FAP) and 33 patients with underlying ulcerative colitis (UC). The control group included 122 consecutive sporadic CRC patients. Cumulative 5-year survival was highest in HNPCC (86%), which is significantly better than in sporadic colorectal cancer (59%, hazard ratio 0.41, P = 0.02). Cancer associated with UC had a 5-year survival rate of 39%, which is significantly less than in sporadic cancer (hazard ratio 1.83, P = 0.03). There was no significant difference in the survival between patients with FAP and patients with sporadic CRC (hazard ratio 1.27, P = 0.5). Exclusion of cases detected by screening examinations slightly reduced the survival rates; 85% for HNPCC, 53% for FAP and 28% for UC. However, the differences between the groups remained significant. The survival of patients with HNPCC was found to be better than that among other groups in this study, which probably relates to the specific tumourigenesis involving DNA mismatch repair dysfunction.