Widespread use of antibiotics and change in pathogenesis altered the bacteriology of infected aortic aneurysms. In the past, bacterial endocarditis was the major source of emboli infecting the aorta. Now, gram-negative sepsis in elderly patients is often the initiating event of infection in atherosclerotic aneurysms. Four cases of gram-negative infection in aortic aneurysms were treated. The etiology, presentation, and surgical management are reviewed. Three abdominal aortic aneurysms were infected during urinary tract sepsis and one infection occurred with Salmonella septicemia. The clinical triad of fever, abdominal pain, and a pulsatile abdominal mass led to a preoperative diagnosis in three of four patients. Debridement of infected tissue and bypass through non-infected tissue planes remain the cornerstones of modern surgical management. Despite prompt diagnosis and proper surgical management, the mortality of gram-negative aortic infection remains high because of early rupture and extensive atherosclerotic disease.