Follow-up studies of 2 groups of patients with idiopathic proctitis show that the survival rate is little affected by the disease. The cumulative probability of extension of the inflammation to the descending colon above the left iliac crest was about 5% at 5 years and 12% at 10 years. Corresponding figures for extension to the hepatic flexure were about 4% at 5 years and 6% at 10 years. The probability of radical surgical treatment was 3--5%.