Urgent surgical operation to treat massive hemmorrhage of colorectal origin was necessary in 12 patients: --colon diverticulosis: 7 cases, --cecal angiodysplasia: 1 case, --pancreatocolic fistula: 1 case, --ischemic colitis: 2 cases, --post-radiation therapy rectitis: 1 case. Lesions exclused from discussion in this report and provoking hemorrhage were colorectal tumors, chronic inflammatsry colitis, rectosigmoid angiomatosis, and post-traumatic or iatrogenic lesions. After a definition of massive hemmorrhage based on pre-operative transfusional requirements, the exploratory procedures necessary for localization of the site of the hemorrhage or for detecting a right colon angiodysplasia are discussed. Bimesenteric arteriography represents the exploration of choice, but its usefulness is limited in patients with several risk factors and an average age of 70 years. The respective values of a barium enema and peroperative endoscopy in this particular context are also discussed. Elective surgery should be performed only when the exact site of bleeding has been determined or when an angiodysplasia is present. Particular problems arise when treating diffuse colon diverticulosis hemorrhage, and that provoked by the association of an angiodysplasia and a diverticulosis, as well as hemorrhagic lesions that may require emergency therapy in much rarer affections: ischemic colitis, pancreatocolic fistula, iliosigmoidal fistula, colorectal varices, colon and rectal ulcers, and colorectal radiolesions.