SummarySix cases of ischemia of the colon and rectum, secondary to operations on the abdominal aorta, are reported, and added to the 33 cases already published.Changes in the colon varied from mild chronic inflammation to complete gangrene of the bowel wall. Clinically, the symptoms and signs varied from transient diarrhea to fulminating bloody diarrhea with fever and toxicity, and from abdominal cramps and distention to advanced peritonitis and death. The diagnosis and treatment must be made early with prompt removal of the involved segment of colon when indicated.The degree of ischemia of the colon and recovery from it depend upon the anatomy of the collateral circulation, the type and degree of the arterial lesion, the duration of occlusive lesions which may or may not permit the development of adequate collateral circulation, the “occlusion time” at operation, the bacteriologic status of the bowel and the postoperative treatment.The major inflow arcs of collateral circulation are the superior to inferior mesenteric artery connection and the inferior mesenteric to hypogastric artery connection. However, alternate routes may be of importance if these two major arcs are compromised.“Ischemic colitis” resembles acute and idiopathic ulcerative colitis. Sigmoidoscopic examination in the two conditions may reveal almost identical findings. The chronic stages of both conditions are similar. “Ischemic colitis” may respond favorably to the same conservative regimen commonly instituted in the treatment of idiopathic ulcerative colitis.