Seventeen consecutive patients with abdominal aortic aneurysms were treated during a 14-year period. Fever was the most common symptom first to appear (12 patients), either as fever of unknown origin or in association with other symptoms. Several factors raise the suspicion of an infected aneurysm: positive blood cultures, erosion of lumbar vertebrae, lack of aortic calcification, aneurysms found in female patients or after a prolonged illness of bacteremia. Staphylococci (41%) and Salmonella (18%) were the most common organisms. Aneurysms with Gram negative organisms exhibited a greater tendency toward early rupture than those with Gram-positive organisms (84% vs 10%), and were associated with a higher mortality. Delay in making the diagnosis adversely affected the death rate. "Infected aneurysm" is suggested as a better term than "mycotic aneurysm," since fungi are rarely involved.