Angiodysplasia of the colon was diagnosed by arteriography in 33 patients. Approximately one fourth of the lesions were located in the left side of the colon. Three patients with sigmoid lesions had a second lesion elsewhere in the gastrointestinal tract. The lesions on the left involved a more extensive segment of bowel than those on the right. Almost one third of the patients were younger than 60, and 2 were in their thirties. The angiodysplasia is the source of the bleeding in most patients, and its resection results in cure.