Follow-up was possible in 71 of 74 patients with idiopathic proctocolitis diagnosed and/or assisted at the Department of Gastroenterology of the Centro Policínico de Almada, between 1973 and 1985. The aim of the present study was to verify the natural history of the disease and if there were statistically significant differences depending on the extension of the disease (proctitis versus colitis). Complications were present in 22 patients (31%): peri-anal (10%), local or intestinal (24%) and extra-intestinal (28%). Fifteen patients (21% of the cases) had hospital admission at least once, and 2 of them (3%) were submitted to surgery. No cases of cancer of the colon and rectum were detected and mortality was nil. Forty-one patients (58%) were assymptomatic at the last observation (45% with colitis and 75% with proctitis). There were statistically significant differences between the group of patients with ulcerative colitis and that of proctitis concerning the total number of complications (p less than 0.001), local complications (p less than 0.01), extra-intestinal complications (p less than 0.05), need for hospital admission (p less than 0.001) and absence of symptoms at the time of last observation (p less than 0.05), thus confirming a better prognosis of the disease when only the rectum is involved.