Colonscopy for investigation of unexplained rectal bleeding

215 colonsocopic examinations were performed on patients with rectal bleeding whose cause had not been determined by barium enema. The probable or definite source of the bleeding was diagnosed in 41% of cases. 13% had a carcinoma, 14% had one or more colonic polyps, 7% had previously unrecognised inflammatory bowel disease. The remainder had various other colonic conditions. The source of bleeding was twice as likely to be found by colonoscopy in patients presenting with frank rectal blood-loss as in those with occult blood. A carcinoma was found twice as often in those patients with diverticular disease as in those without this condition. A lesion was discovered in the majority of patients who had had two or more negative barium enemas. These results emphasise the importance of rectal bleeding as a symptom of colonic abnormality and the value of colonscopy in its investigation in patients where the results of radiology are negative.