To establish further insight into the relevance of intraoperative bacterial cultures of abdominal aortic aneurysm contents a study was performed of the rate of occurrence of prosthetic graft infection after aneurysm repair.Bacterial cultures were obtained from 216 patients, who were followed up for more than 3.5 years after operation and studied retrospectively in a single center analysis.Thrombus cultures yielded bacteria in 55 of 216 (25.5%) cases, including 11 of 44 (25%) cases with ruptured aneurysms. Prosthetic infections (4 of 216; 1.9%) occurred more frequently (p0.02) in patients with positive thrombus cultures (3 of 55; 5.5%) than in patients with negative cultures (1 of 161; 0.6%). In two patients the species isolated from the thrombus was also cultured from the vascular prosthesis, although in one graft infection other organisms were also isolated.The presence of bacteria in the intraluminal thrombus does not appear to be an important factor in the development of graft infection after primary elective and urgent abdominal aortic aneurysm repair. Therefore routine intraoperative cultures are unnecessary unless clinical signs of infective aortitis are present.