A 54-year-old male suddenly developed cramping abdominal pain followed by diarrhea. A segmental narrowing with multiple mucosal ulcers of the colon near the splenic flexure was noted on both barium enema and fiberoptic colonoscopy. Cramping abdominal pain and diarrhea persisted, associated with a body weight loss of 13 kg. Four months later, angiography revealed an isolated, complete occlusion of the left colic artery near the point of branching from the inferior mesentery artery. The artery was biopsied and the severely strictured colon was removed. The artery showed an eccentric organized hematoma between the outer media and the adventitia. The lumen was occluded by organized thrombi. The pathologic findings were those of an organized dissecting hematoma (aneurysm), probably caused by segmental mediolytic arteriopathy.