Angiodysplasia is a recently recognized important cause of lower intestinal bleeding in older patients. Although angiography is an established procedure for the diagnosis of angiodysplasia, colonoscopy is being used increasingly for evaluation of lower intestinal bleeding. In order to define the nature of bleeding due to angiodysplasia and the appropriate role of colonoscopy, 80 patients diagnosed by angiography, pathology, or colonoscopy were reviewed. Bleeding attributable to angiodysplasia varied from acute life-threatening hemorrhage to occult blood in stools. Thirteen patients with angiodysplasia had no bleeding and were identified incidentally by colonoscopy performed for other indications. Eighty-nine percent of the lesions were located in the right colon and there was a mean of 1.5 angiodysplastic lesions per patient. The sensitivity of colonoscopy compared to angiography and pathology was 68% overall and 81% when the colon was completely examined and lesions were located in the colon. The predictive value of a positive colonoscopic diagnosis was 90% in this population. Colonoscopy should be employed as an initial study in patients with chronic or mild acute rectal bleeding.