Klippel-Trenaunay syndrome (KTS) is a congenital vascular anomaly characterized by limb hypertrophy, cutaneous hemangiomas, and varicosities. GI hemorrhage is a potentially serious complication secondary to diffuse hemangiomatous involvement of the gut. We report on three patients with KTS who presented with transfusion-dependent anemia and life-threatening bleeding due to extensive cavernous hemangiomas involving the rectum. Two patients were treated by proctocolectomy and coloanal anastomosis, which preserved anal function while controlling bleeding. The third patient required an abdominoperineal resection because of extensive rectal, perianal, and perineal angiomatosis. The literature on the evaluation and management of GI hemorrhage in KTS, particularly of colorectal origin, is reviewed.