From 1975 through 1979, 29 members of The Cleveland Vascular Society operated on 1049 patients with abdominal aortic aneurysms; of these, 152 ruptured aneurysms. The postoperative mortality rate was 38% (58 of 152). In 27% (41 of 152) of the patients, a diagnosis was made prior to rupture, and the average interval from diagnosis rupture was 16 months. A history of diabetes, hypertension, or a single myocardial infarction (MI) prior to rupture was not associated with an increased mortality rate. Patients with a history of more than one MI prior to rupture had a 75% (six of eight) mortality rate. The average time from onset of symptoms to examination was 2 days 10 hours. When the initial diagnosis was correct, or an intra-abdominal disease was at least suspected, the mortality rate was 35% (47 of 135). When the initial diagnosis was incorrect and a cardiopulmonary or cerebral cause was suspected, the mortality rate was 75% (13 of 17). When the diagnosis was incorrect, the interval from diagnosis to surgery was 2 1/2 days. With only intramural bleeding or a small hematoma in the area of rupture, the mortality rate was 17% (4 of 24); when the hematoma was more extensive, the mortality rate was 43% (55 of 128). This study encompassed a large number of operations performed in a metropolitan area during a relatively short period of time, during which there had been few changes in operative technique or supportive measures. It demonstrated that the most critical factors influencing survival were correct initial diagnosis, the extent of the hematoma, and the history of more than one preoperative MI.