Interrupted aortic arch (IAA) is often related developmentally to subaortic obstruction (SAO). When severe, SAO must be addressed in surgical management of IAA. From 1990 to 1993, 25 neonates presented for initial surgical management of IAA complexes. Associated lesions were ventricular septal defect (VSD) with or without atrial septal defect (19 patients), truncus arteriosus (3 patients), tricuspid atresia with transposition of the great arteries (1 patient), aortic atresia with VSD (1 patient), and d-transposition of the great arteries with VSD (1 patient). Overall hospital mortality was 20% (five deaths). One death was related to sepsis and two to sudden hemodynamic decompensation (a 2-kg premature infant after arch repair and VSD closure and a neonate with IAA-truncus arteriosus after arch repair and truncus repair with aortic root replacement). Two deaths were related to low cardiac output in patients with severe subaortic narrowing (< 3 mm by two-dimensional echocardiography), which was not addressed surgically. Of 10 additional patients judged preoperatively to have severe SAO, 1 underwent resection of the infundibular septum together with VSD closure and arch reconstruction, and 9 underwent a modification of Norwood's operation with arch reconstruction and proximal pulmonary artery to aortic anastomosis (7 with systemic to pulmonary artery shunts and 2 with right ventricle to pulmonary artery outflow tract reconstruction). One patient died 2 months after surgery of staphylococcal sepsis. All 9 others were discharged well. Subaortic narrowing is a physiologically important element of IAA complexes. When SAO is severe, satisfactory initial palliation can be achieved by a modification of Norwood's operation.