A study of 100 patients experiencing 144 episodes of bleeding from colonic diverticula was made. In 16, colonic bleeding was the first manifestation of diverticular disease. Surprisingly, 42 had only black, tarry stools while 58 had bright red rectal bleeding. Sixty bleeding episodes (41.5%) were massive and necessitated transfusion of more than 1,500 ml of blood. Fifty-three (37%) did not lead to transfusion. Only five were associated with signs of acute diverticulitis. Although only 19 patients, all initially treated with a medical regimen, required operation, they had often bled too much (average 5,260 ml), too long and too often before operative intervention. Frequently the wrong operation was performed. This study demonstrates that local resection is adequate only if disease is confined to a single area which is bleeding. When disease is extensive, total abdominal colectomy with ileoproctostomy is the procedure of choice.