This report summarizes the clinical, pathological, and surgical aspects of ruptured abdominal aortic aneurysm. The significant risk of rupture of these aneurysms is well documented. Although large aneurysms are more prone to rupture, the risk of rupture of small aneurysms less than 4 cm in diameter is well established. While most aneurysms are a result of atheroselerosis, a small number are mycotic in origin or secondary to a dissection trauma or previous aortic surgery. Rupture of abdominal aneurysms occurs into the retroperitoneum in about 3/4 of cases, and into the peritoneal cavity in the remainder. Occasionally rupture occurs into the small bowel or the inferior vena cava with fistula formation. The classical clinical features are abdominal or back pain, hypotension, and a pulsatile tender abdominal mass, but in many cases diagnosis has been delayed because of atypical presentations, in particular the absence of hypotension. Successful treatment requires immediate operation with control of the proximal abdominal aorta. Graft replacement is then performed. Avoidance of technical problems is essential, in particular damage to the great veins. Utilizing these principles we have achieved a major reduction in mortality rate in our own experience. In a series of 61 patients, overall mortality was only 14.8%. The causes of death were related to preoperative hypotension causing acute myocardial infarction, renal failure, and respiratory failure. The major factor~ responsible for these improved results were immediate operation with rapid proximal aortic control, avoidance of left thoracotomy, absence of technical errors, and expeditious completion of the surgical procedure. Despite these improved results, emphasis must continue to be placed on prevention of rupture by diagnosis and treatment of the unruptured aneurysm.The purpose of this report is to summarize the clinical, pathological, and surgical aspects of ruptured abdominal aortic aneurysm. The significant risk of rupture of an abdominal aortic aneurysm has been well documented. In the classical study of Estes [1] published in 1950, survival in a group of patients followed without surgical resection was only 18.9% at 5 years; 63.3% of deaths were due to rupture of the aneurysm. More recent reports have confirmed these findings. In a study [2] of 223 patients with abdominal aortic aneurysms that were not operated upon, the survival rate was only 54.3% at 1 year and 17.2% at 5 years, and 35% of all deaths were due to rupture of the aneurysm. In another report of 52 patients followed up without operation until all were dead, 43% of deaths at 1 year were due to rupture of the aneurysm, and by 10 years 52% of the patients had died from rupture [3].The risk of rupture has been related to the size of the aneurysm. Large aneurysms have been observed to rupture mo,'e frequently than small aneurysms. The incidence of rupture of aneurysms over 10 cm in diameter is about 6 times that of aneurysms 4 cm or under in diameter [2,3]. However, even very small aneurysms may ruptu...