Unilateral pulmonary agenesis is a rare congenital anomaly and is frequently associated with other congenital anomalies. We report a case of left pulmonary agenesis associated with congenital tracheal stenosis in a newborn infant. Simple chest radiographs showed an overinflated right lung and mediastinal shifting to the left side. Chest CT and reconstructed three-dimensional images showed left pulmonary agenesis and tracheal stenosis. These anomalies of the tracheobronchial system were confirmed by bronchography.