Superior mesenteric artery embolism or thrombosis and nonocclusive ischemia are the most frequent causes of mesenteric ischemia. Symptoms out of proportion to the physical findings, leucocytosis, and metabolic acidosis suggest the diagnosis. A high index of suspicion, aggressive resuscitation and correction of metabolic derangements, early angiography, and operative intervention are necessary if the current high mortality rates are to be reduced.