The isolated unilateral absence of a proximal pulmonary artery is a rare congenital lesion with a diverse clinical presentation. If the connecting ductus arteriosus closes after birth, the ipsilateral pulmonary artery will lose its source of blood supply, resulting in hypoplasia or obliteration of intrapulmonary vessels. Despite a seemingly benign early clinical course, a significant number of untreated patients will develop pulmonary hypertension, hemoptysis, and recurrent respiratory infections. Early detection and surgical repair provides restoration of physiologic pulmonary circulation, regression of pulmonary hypertension, and the potential for normal distal pulmonary vascular development.