In a prospective study, the occurrence of angiodysplasia was investigated by total colonoscopy in 1938 patients. Angiodysplasia was found in 59 patients, i.e. 3%. 12 out of 59 patients were admitted for acute or chronic peranal hemorrhage or anemia. 47 out of 59 patients were asymptomatic. The site of the lesions was as follows: cecum 37%, ascending colon 17%, transverse colon 7%, descending colon 7%, sigmoid colon 18% and rectum 14%. Histological confirmation was obtained in 15 out of 37 biopsies. The endoscopic appearance was variable, most of the vascular dilatations being smaller than 5 mm (n = 47), with a homogeneous (n = 35) or inhomogeneous (n = 24) structure and a regular (n = 34) or irregular (n = 25) border. The lesions were single (n = 34) as well as multiple (n = 25), they were usually flat (n = 54), seldom slightly prominent (n = 5). Concomitant pathological findings in the bowel were diagnosed in 33 out of 59 patients: diverticula in 32%, adenomas in 24% and carcinomas in 8.5%. Right hemicolectomy for bleeding angiodysplasia is indicated only if endoscopic therapy has failed and other colorectal sources of bleeding, and especially angiodysplasia in the left colon and rectum have been excluded by endoscopy or angiography.