Ascending colon angiodysplasia is a frequent cause of colorrhagia or chronic blood loss in old patients, but also possible under the age of 55. Angiodysplasia diagnosis is often underestimated. For a long time colorrhagia or lower intestinal bleeding were generally diagnosed like diverticular bleeding. This conclusion was the result of several conditions: the conservative management of distal gastrointestinal bleeding is in most cases successful; the double dye clysma was the first and the main diagnostic procedure for many years and the result was a not correct diagnosis of diverticular bleeding since large bowel diverticulosis is always present in the elderly. The authors report on three cases of low intestinal bleeding where the diagnosis of angiodysplasia in the first patient was performed by upper mesenteric artery arteriography, in the second by preoperative colonoscopy and after confirmed by the histology of the specimen and in the last one by colonoscopy performed in emergency and after intestinal irrigation. The first patients refused the operation; the second had right hemicolectomy and the third one had a spontaneous stop of bleeding. According to their clinical experience the authors suggest that colonoscopy performed in emergency or intraoperative is the first choice diagnostic procedure: it can detect the source of bleeding between right or left colon. Arteriography often shows vascular images characteristic for angiodysplasia or other vascular malformations but, in our experience, it may be absolutely not diagnostic. Colonoscopy performed in emergency during bleeding or per-operative is the best procedure in order to diagnose the source of bleeding. Emergency colonoscopy can distinguish if the blood is coming from the right or left colon and in our experience, colonoscopy during bleeding is always possible because blood has a cathartic effect. In case of emergency operation pre-operative colonoscopy can usually detect the source of bleeding. A double dye clysma, whether barium or hydrosoluble doesn't give a diagnostic support in low intestinal bleeding; on the contrary it can prevent a correct arteriographic and endoscopic evaluation. At last histopathological findings on the specimen are conclusive for the diagnosis.