A patient with pulmonary tuberculosis and a constricting transverse colon lesion on barium enema was found at colonoscopy to have a 1.5 X 3.0 cm ulcer with irregular, edematous borders. Multiple colonoscopic biopsies of the ulcer revealed acid-fast bacilli with absence of granulomas. Previously, the diagnosis of colonic tuberculosis had been thought to require laparotomy for confirmation. The authors now suggest that colonoscopic biopsy may be a desirable alternative in selected cases.