Abdominal aortic aneurysm (AAA) is distinctly uncommon in infants and children, and usually results from infection, iatrogenic trauma, vasculitis, connective tissue disorder, or tuberous sclerosis. Congenital "primary" neonatal AAA is exceedingly rare. The few reported cases of repair of congenital AAA describe use of synthetic graft material or aneurysmorrhaphy. We report the first successful treatment of a known 6 cm congenital infrarenal AAA repaired with a 5 mm cryopreserved allograft in a 4-month-old infant girl. The graft was pretreated with an antigen reduction process (SynerGraft), which preliminary studies suggest may inhibit allograft degeneration. The postoperative course was unremarkable. Lower extremity pulses and results of duplex ultrasound flow studies remained excellent at 14-month follow-up. Panel reactive antibodies against class I alloantigens remain negative. The use of an antigen-reduced allograft provides an acceptable conduit, which potentially may decrease allograft degeneration and relative graft stenosis associated with growth of the child, but requires follow-up.