Forty-nine patients with acute mesenteric ischemia have been treated during the past 15 years. The overall mortality rate was 65%; the prognosis varied with the cause of disease. None of the 12 patients with primary thrombosis of the mesenteric arteries, 5 of 14 with spontaneous embolization, and 2 of 4 with arterial occlusion subsequent to diagnostic angiography survived. Seven of 11 patients with primary mesenteric venous thrombosis and 2 of 7 patients in whom mesenteric ischemia was related to low flow unassociated with occlusion of either the major arteries or veins survived. The only patient with occlusive arterial vasculitis survived. Thirty-one of these 49 patients presented with peritoneal signs. The serum glutamic oxaloacetic transaminase, lactic dehydrogenase, and creatine phosphokinase levels were significantly elevated in patients with nonocclusive ischemia and less elevated in patients with arterial or venous thrombosis. By contrast, the enzyme levels were frequently normal in patients with arterial embolization. Angiography was diagnostic in all four patients who were evaluated with this procedure--three patients with arterial embolization and one patient with nonocclusive ischemia. This procedure should be used more frequently, especially when embolization is suspected. The value of reexploration was assessed. There were 17 reexplorations, with only three contributing to survival (17.7%). Two patients with mesenteric venous thrombosis and one patient with arterial embolization benefited from resectional therapy during reexploration. The study emphasizes that diagnostic criteria, therapy, and prognosis can be correlated with the etiologic factor.