Spiral CT angiography was performed in a patient suspected of having pulmonary embolism. The right pulmonary system was normal. The left arterial system was small but patent. The left upper lobe was small and hyperlucent. The left lower lobe was collapsed and contained bronchiectasis. The bronchi were patent. High resolution CT in inspiration and expiration confirmed air trapping in the left upper lobe. A diagnosis of Swyer-James syndrome of the left upper lobe was made.