SummaryA case of ischemic colitis proximal to an obstructing carcinoma of the colon is presented. The first description of the blood vessels in such cases is included. The necessity for preoperative or operative diagnosis is stressed. Significant mortality and morbidity from suture‐line disruption occur in the absence of proper diagnosis. Frozen section of the proximal margin of resection is recommended to determine whether further proximal resection should be done. Particular emphasis is placed on evaluation of the blood vessels in the submucosa.