Multicystic encephalomalacia (ME) usually results from severe hypoxic-ischemic brain damage occurring during the late third trimester of gestation and birth. We report on a case of congenital ME due to a congenital anomaly of the aortic origin of brachiocephalic vessels resulting in subclavian steal syndrome. A 5-day-old term neonate presented with microcephaly and overlapping cranial sutures. Both arms were developed normally. Magnetic resonance imaging of the brain showed extensive bilateral supratentorial ME. Color duplex sonography of the aortic arch and the intracranial and extracranial vessels revealed a stenosis at the origin of the left common carotid artery and atresia of the origin of the left subclavian artery resulting in left-sided subclavian steal syndrome and retrograde perfusion of the basilar artery. Total cerebral blood flow volume was reduced to 22 mL/min. Severely reduced cerebral blood flow volume resulted from left carotid artery stenosis and atresia of the origin of the left subclavian artery with consecutive subclavian steal. Infratentorial brain structures and the left arm remained intact, but supratentorial brain structures were severely affected with ME.