The endoscopic spectrum of late radiation damage to the rectosigmoid colon in 90 patients seen over a 10 year period (1973-1983) is presented. The main endoscopic findings were abnormalities of the mucosa with characteristic telangiectasis, luminal narrowing, superficial or deep solitary ulcers or more extensive diffuse ulceration and fistulae. A knowledge of the pathognomonic features may lead to early detection and treatment.