A series of 12 patients with relative sparing of the rectum in ulcerative colitis is analyzed. Half were recorded as having normal sigmoidoscopic appearance and, in every case, double-contrast barium enema showed an apparently normal rectum but an abnormal colon. Rectal biopsy showed changes compatible with ulcerative colitis in all cases, though in four, changes were slight. Thus, complete histologic sparing of the rectum was not observed. In four of six patients treated by colectomy and ileorectal anastomosis, inflammation of the retained rectum required medical or surgical treatment.