Vascular anomalies of the aortic arch causing tracheoesophageal obstruction are relatively common. We believe this case of obstruction to the right main stem bronchus by an anomalously placed left pulmonary artery is unique. A white baby boy, aged 9 days, was admitted to the Children's Memorial Hospital on April 16, 1953, because of attacks of dyspnea and cyanosis since birth. The infant weighed 9 lb. 8 oz. (4,309 gm.) and had been delivered spontaneously on April 7, 1953, at Michael Reese Hospital after a normal pregnancy. Difficulty in respiration was present immediately after birth and was not improved by the usual tracheal toilet. Because of continuing dyspnea and cyanosis, the child was placed in an incubator with humidified oxygen. Abnormal physical findings consisted of sternal retractions with each breath, decreased breath sounds on the right side, and displacement of the heart to the left. Roentgenograms made 12 hours after birth