An abdominal aortic aneurysm is a rare disease in the paediatric population and is mainly caused by intrauterine infection, connective tissue diseases, such as Ehlers-Danlos syndrome and Marfan’s syndrome, and iatrogenic trauma due to umbilical artery catheterization. Although several cases have been reported in the English literature, they were rarely diagnosed prenatally. Vascular obstruction in utero is also believed to be the major cause of porencephaly. Recently, gene mutations have been reported as the cause of both the above-mentioned diseases. We present a prenatally diagnosed case of congenital abdominal aortic aneurysm with porencephaly.