Institutes of Health, Bethesda, Maryland Infected (mycotic) aortic aneurysms are infrequent and, without surgical intervention, usually lead to uncontrolled sepsis or catastrophic hemorrhage. Symptoms are frequently absent or nonspecific during the early stages, and a high index of suspicion is essential to make the diagnosis. Surgery performed after rupture carries high morbidity and mortality rates. Bacterial endocarditis with streptococcus pyogenes was the most common cause of infected aortic aneurysm in the pre-antibiotic era. Today, arterial trauma due to iatrogenic manipulation and depressed immunocompetence have become more common risk factors. Staphylococcus aureus and Salmonella are the most frequent bacteria identified. The authors' recent experience in six patients with infected aortic aneurysms who underwent arteriography and computed tomography was reviewed and these diagnostic methods compared. Computed tomography was found to be more sensitive in the diagnosis of the early stages of the disease, allowing for follow-up by serial scans in a noninvasive and less costly manner. Successful treatment, in four of these patients, was accomplished by aneurysmal resection and extra-anatomic bypass or in situ prosthetic reconstruction. A higher clinical awareness of this disease, leading to early computed tomography evaluation and prompt surgical intervention under appropriate and intensive antibiotic therapy, appears to offer the best chance of survival in patients with this difficult condition.