The pulmonary sling or aberrant left pulmonary artery has an incidence of 3% to 6% of all anomalies of the aortic arch system. We report a boy with coexistence of a normal and an anomalous left pulmonary artery. Associated congenital anomalies were coarctation, mitral stenosis, and imperforate anus. Cardiac catheterization and angiocardiography at the age of 5 months demonstrated an inconspicuous pulmonary trunk dividing into left and right branches. There was a normal right pulmonary artery, and a main left pulmonary artery supplying the left upper lobe, lingula, and anterior segments of the left lower lobe. In addition, an anomalous left lower lobe artery originated from the proximal right pulmonary artery, passed inferior to the tracheal bifurcation to the left supplying posterior segments of the left lower lobe. Chest X-rays and bronchoscopy could not detect any malformation of the trachea and pulmonary lobulation. There are only three reports of partial anomalous origin of the left pulmonary artery, and only one had a similar course of the accessory artery. This report is the first to present selective angiography and echocardiographic findings of the partial anomalous left pulmonary artery. The development of the partial anomalous pulmonary artery can be explained by the plexiform nature of the primary pulmonary vascular bed and can help to understand the embryology of the pulmonary arteries.