The present mortality rate of more than 80% for patients with superior mesenteric arterial thrombosis or embolism will remain unacceptable until earlier diagnosis is achieved. Although leukocytosis is often an early feature and may seem elevated out of proportion to the severity of the illness, the later developments of abdominal rigidity, intestinal paralysis, and vascular collapse indicate transmural gangrene and peritonitis. At this stage, the eventual high mortality of acute ischemia is established whatever the urgency of the operation or the skill with which it is performed. The syndrome must be suspected immediately when a patient in an older age group complains of sudden abdominal pain in the presence of associated cardiac arrhythmia, valvular disease or congestive heart failure, particularly if other sites of peripheral embolization are identified.