Aneurysm of the main pulmonary artery is a rare clinical entity that can be congenital or acquired. Most cases occur in association with other congenital malformations, severe pulmonary hypertension, vasculitides, infectious agents, or collagen vascular disorders. We report here a pediatric case of left pulmonary artery aneurysm associated with valvular pulmonary stenosis and a hypoplastic right pulmonary artery, which we confirmed via multidetector computed tomography angiography.