Patients requiring emergency operation for severe acute colonic hemorrhage usually arrive in the operating room inadequately studied and the point of bleeding not known. A well planned procedure for making an operative diagnosis is lacking. The fact that diverticular disease is the most common cause of massive colonic bleeding, dominates the surgical management of this problem. A critical interpretation of the color and the consistency of the stools must be made by the surgeon. Since the bleeding lesion is usually otherwise clinically silent, the character of the stools may be the only indication of the level of bleeding and the rate and the amount of the blood loss. A proctoscopic examination, followed by an emergency barium enema study if possible, is always done before subjecting a patient to laparotomy. The indications for emergency operation include acute exsanguinating hemorrhage, less severe but persistent colonic bleeding and recurrent colonic bleeding. The steps for the operative diagnosis and the surgical procedure utilized for a specific situation are discussed.