Four neonates with hypoplastic left heart syndrome (HLHS) were found to have innominate artery steal syndrome (IASS) following stage I palliation with a modified Blalock-Taussig (B-T) shunt. All patients presented in the early postoperative period with a persistent supplemental oxygen requirement. Two-dimensional echocardiography with Doppler flow analysis and cardiac catheterization with angiography demonstrated obstruction at the origin of the innominate artery. This obstruction was associated with intermittent retrograde flow through the right vertebral and common carotid arteries into the distal innominate artery and modified B-T shunt. An ascending neoaorta to right pulmonary artery shunt, with takedown of the B-T shunt, was performed in two of the patients. The other two patients were treated with percutaneous balloon dilatation of the obstructed area. Both procedures improved arterial blood oxygen saturations and eliminated the need for supplemental oxygen. In three of four patients, the left common carotid artery was found to be larger than the right. All four patients developed microcephaly, and one patient had encephalomalacia in the distribution of the right anterior and middle cerebral arteries. The development of IASS following stage I palliation for HLHS and the association of neurologic sequelae from this complication are discussed.