Anomalous origin of 1 of the branch pulmonary arteries from the aorta with 2 normal semilunar valves (hemitruncus) is a rare entity. There have been several small case series reported. We report here our single-institution surgical experience with hemitruncus from 1982 to 2006. A retrospective case review of all cases of conotruncal anomalies at Children's Hospital Boston revealed 16 patients with hemitruncus. Ten patients had surgery in the neonatal period (<30 days), 4 at 1 to 6 months, 1 at 8 months, and 1 at 2 years. Diagnosis of hemitruncus was the indication for operation in all but 1. Fourteen of the 16 had anomalous right pulmonary artery from aorta, and 2 had left pulmonary artery from aorta. Common associated anomalies included patent foramen ovale in 14, patent ductus arteriosus in 11, and ventricular septal defect in 4. All patients had elevated right ventricular pressures with systemic pressures in 5 and suprasystemic pressures in 9. There was 1 operative death in this series in an infant who died from sepsis following ligation of a tracheoesophageal fistula. One patient required reoperation for supravalvular aortic stenosis and right pulmonary artery stenosis 1 year postoperatively. Three patients required 4 catheter-based interventions postoperatively. At 20 years, survival by Kaplan-Meier was 93%; freedom from reoperation, 93%; and freedom from catheter reintervention, 79%. Early repair of hemitruncus results in excellent hemodynamic and anatomic results. Survival is excellent, with a low incidence of reoperation or reintervention.