Probability of rupture of an abdominal aortic aneurysm after an unrelated operative procedure: a prospective study. It has been assumed by some authors that patients with abdominal aortic aneurysms may be at increased risk of rupture after unrelated operations. From July 1986 to December 1989, 33 patients (29 men, 4 women) with a known abdominal aortic aneurysm underwent 45 operations. Twenty-eight patients had an infrarenal abdominal aortic aneurysm, and five patients had a thoracoabdominal aneurysm. The abdominal aortic aneurysm ranged in transverse diameter from 3.0 to 8.5 cm (average 5.6 cm). Twenty-seven patients underwent a single operation, and six patients had two or more (range of 1 to 6). Operations performed were abdominal (13); cardiothoracic (9); head/neck (2); other vascular (11); urologic (7); amputation (2); breast (1). General anesthesia was used in 29 procedures, spinal/epidural in 6, and regional/local in 10. One postoperative death occurred from cardiopulmonary failure. One patient died of a ruptured abdominal aortic aneurysm at 20 days after coronary artery bypass (1/33 patients [3%]; 1/45 operations [2%]). Fourteen patients had repair of their abdominal aortic aneurysm at a later date, an average of 18 weeks after operation. Four patients had abdominal aortic aneurysm considered too small to warrant resection (average 3.6 cm). Four patients were considered at excessive risk for elective repair. The five thoracoabdominal aneurysm were not repaired. Four patients are awaiting repair. During this same 40-month period, two other patients, not known to have an abdominal aortic aneurysm, died of a ruptured abdominal aortic aneurysm after another operative procedure, at 21 days and 77 days. All three ruptured abdominal aortic aneurysms were 5.0 cm or greater in transverse diameter. 