Colonoscopy in the diagnosis of unexplained rectal bleeding.

Three hundred six patients with unexplained rectal bleeding were examined by colonoscopy. Significant lesions were found in 30% including polyps having a diameter of 0.5 cm or larger in 14%, carcinoma in 8%, and a small number of patients with inflammatory bowel disease, vascular formations, and radiation colitis. Colonoscopic findings in a large subgroup of patients with diverticulosis established by barium enema did not differ significantly from those of the group as a whole. Significant lesions were also identified in 22% of small subsets of patients with occult bleeding or unexplained melena.