Mycotic aneurysms of the aorta are uncommon in babies and children. Prior to the development of antibiotics, most mycotic aneurysms were seen secondary to bacterial endocarditis, but this is now uncommon. Instead, more cases have been reported as complications of umbilical artery catheters in newborns. Five cases of mycotic aneurysms in children were studied, 2 of them secondary to umbilical artery catheters. One patient had coarctation of the aorta, and the other patients had different sources of infection. Three patients were treated surgically with good results after antibiotic therapy. One patient died of sepsis before the aneurysm was diagnosed. The 5th patient was treated elsewhere and now has a recurrent aneurysm. A combination of aggressive medical and early surgical therapy may save a high percentage of these patients.