Ischemic colitis occurs when the blood supply to descending and sigmoid colons is impaired as a result of surgery for abdominal aortic aneurysms. Selective and routine reimplantation of the inferior mesenteric artery was assessed to clarify which was more effective in preventing this complication. Fifty patients who underwent surgery for non-ruptured abdominal aortic aneurysms over a 5-year period were reviewed. Four patients who had occluded inferior mesenteric artery were excluded from comparison. In 27 patients operated in the first half of the period, stamp pressure of the inferior mesenteric artery was measured, and arterial blood flow was detected in the mesocolon with a Doppler ultrasonic flowmeter. Nine patients with impaired blood flow underwent reimplantation of the inferior mesenteric artery. The inferior mesenteric artery of all 19 patients operated in the second half was reimplanted. Operative blood loss, operation time, and postoperative course were compared in the selective and routine reimplantation gruops. There were no significant differences between the two groups in distribution by age, sex, incidence of previous laparotomy, or preservation of both internal iliac arteries. Operative blood loss and operation time did not increase significantly after routine reimplantation of the inferior mesenteric artery was begun. Ischemic colitis was not observed in either group. Comparison of the postoperative course in the two groups showed no significant difference in the time required to resume oral feeding or in the number of days from operation to discharge. Further studies are recommended, comparing selective and routine reimplantation of the inferior mesenteric artery.