The pattern of mortality has been examined in a series of 676 patients with ulcerative colitis under long-term review to identify excesses or deficits in mortality for all causes of death in relation to the general population. The mortality risk for the whole series was 1.7 times that of the general population (p less than 0.001). Most of the excess mortality could be attributed to diseases of the digestive system. There was a heavy burden of mortality during the first year afer diagnosis and the first year after radical surgery. The significance of the excess of cancer deaths was due to the inclusion of patients who were diagnosed with cancer at first referral. In man there was a deficit of circulatory system deaths particularly those with early onset ulcerative colitis treated by panproctocolectomy after 40 yr of age. Mortality from all other causes including breast cancer showed no significant difference from that expected in the general population.