Abdominal aortic aneurysms are distinctly uncommon in infants and children. These aneurysms, which are idiopathic in nature without any definite predisposing factors, are exceedingly rare. We present the case of a giant idiopathic congenital infrarenal abdominal aortic aneurysm with impending rupture in a 23-month-old boy, which was successfully treated with surgical repair using a cryopreserved cadaveric allograft. To the best of our knowledge, this is the oldest case and the third successful treatment of an idiopathic congenital abdominal aortic aneurysm repaired with a cryopreserved allograft in infants and children. Continued follow-up with multimodality imaging is required.