Abdominal aneurysms are rare in children and are usually found in association with congenital cardiac or aortic malformations, connective tissue disorders, trauma, or previous arterial catheter placement. A 4-year-old girl who had a common iliac artery aneurysm, who had no history of arterial catheter placement or trauma, and who had no evidence of Marfan's or Ehlers-Danlos syndrome, arteritis, coarctation of the aorta, or other diseases associated with childhood aneurysms is presented. Resection of the aneurysm and arterial reconstruction were performed without the use of prosthetic material or vein graft. Pathologic examination showed no evidence of inflammation or medial degeneration in any of the layers of the arterial wall. This is the fourth report found in the literature of documented idiopathic abdominal aneurysm in a child. The conditions associated with abdominal aneurysms in childhood are discussed, and the literature is reviewed.