The cumulative risk of developing colon cancer in patients with ulcerative colitis has been stated to increase 10%-20% for every decade of duration of disease after 10 yr. We reviewed the clinical course of 673 patients with inflammatory bowel disease restricted to the colon who were seen by the authors since 1955. A subset of 258 patients with a diagnosis of ulcerative colitis established before 1970 and followed by the authors was studied by both the classical life table and a generalized approach to estimate the risk of colorectal carcinoma. Only nine instances of colorectal carcinoma occurred. Using the former method and eliminating 3 patients referred with known colorectal carcinoma, the actuarial risk for developing this complication for all patients, regardless of extent of disease, was computed to be only 6.6% at 26 yr and 11.4% at 32 yr following the onset of ulcerative colitis. The cumulative probability of colorectal carcinoma among patients with universal colitis at 26 yr was 19.7% by the generalized method and 11.6% using the standard life table. The generalized approach consistently gave higher risk estimates due to a smaller number of patients in the denominator of the risk calculation. Using an alternative method, we calculated cancer risk from the date first seen for patients with universal extent and a history of greater than or equal to 10 yr of disease (means = 17.4 yr). The magnitude of the resulting colorectal carcinoma risk was even less than previously reported in hospitalized patients. This method is more suited for colorectal carcinoma risk assessment of a large series of ulcerative colitis patients seen in private practice and the results should modify the fear of cancer development in these patients.