A clinical review of 204 cases of idiopathic ulcerative colitis (IUC) seen in an insurance hospital in Istanbul during a period of nine years is presented. The criteria of diagnosis were based on history and results of rectosigmoidoscopic, biopsy, and barium-enema examinations. In the majority of cases (74 per cent), the disease manifested in the mild form, despite a history of one to five years' duration at the time of diagnosis. These patients usually had single attacks, with recovery in reponse to treatment. The mortality rate for the whole series was 3.9 per cent. Death occurred in eight cases of patients who had the severe form of the disease involving the entire colon, with fulminating courses. One additional death was due to an accident. Treatment consisted of a high-protein, low residue diet, vitamins, rest, sulfa drugs and steroids. Azathioprine, in addition, was used in fulminating cases. Surgery supplemented medical therapy in 19 cases. Indications for surgical treatment were resistance to medical management, cancer, and polyposis. Only two patients (1.0 per cent) were found to have cancer during the follow-up period. These two were operated upon. Idiopathic ulcerative colitis is not a rare entity; with awareness and use of appropriate diagnosis facilities, more cases are being discovered.