Acute mesenteric ischemia represents one to two percent of all gastrointestinal illnesses. There are three possible causes of acute arterial mesenteric ischemia: embolism, thrombosis, and nonocclusive mesenteric insufficiency. The key to early diagnosis is a high index of suspicion. The classic clinical picture of obvious cardiac disease, sudden onset of severe abdominal pain and gastrointestinal emptying, is not always present. Serum markers and plain films are often nondiagnostic but may suggest acute arterial mesenteric ischemia. Angiography establishes the diagnosis and allows for planning of aortomesenteric bypass, if indicated. Papaverine is immediately instilled to decrease splanchnic vasoconstriction. Embolic and thrombotic disease is treated by laparotomy with re-establishment of visceral perfusion. Only after blood flow is restored is nonviable bowel resected. Clinical methods of assessing intestinal viability include Doppler scanning, intravascular dyes, and tissue oximetry. The decision to perform a second-look laparotomy is made prior to closure of the abdomen. Pharmacologic treatment is the mainstay of nonocclusive ischemia. Surgery is reserved for clinical deterioration. Survival is dependent on the cause and extent of occlusion as well as the rapidity of diagnosis and therapy. Bowel necrosis results in mortality rates between 80 percent and 95 percent.