Introduction: Swyer-James syndrome (SJS) is a rare cause of a unilateral hyperlucent hemithorax. The condition usually follows a viral or bacterial respiratory infection in infancy or childhood. Most patients are clinically asymptomatic. However, some patients can present with repeated pulmonary infections, dyspnea, or hemoptysis. We report a fifteen-year-old boy with SJS. Case: A fifteen-year-old boy presented with acute onset dyspnea, cough and chest discomfort with low grade fever. He had treated for pneumonia due to adenovirus and Mycoplasma pneumoniae at the age of 4 years. There were no significant problems after pneumonia at the age of 4 years. He has no family history of pulmonary or allergic diseases. On examinations, blood pressure of 160/80 mmHg, pulse rate of 107/min, respiratory rate of 20/min and saturation of 97% on room air were checked. Lung sound was clear and decreased breath sound at the left lung. The remainder of physical examination was normal. Lab findings showed a WBC of 8600/mm3 (neutrophil 76.1%, lymphocyte 7.5%, eosinophil 2.2%), serum total IgE of 47 IU/ml. On blood gas analysis of vein, pH 7.38, PCO2 40.9mmHg, PO2 55.8mmHg and bicarbonate 24.5mEq/L were checked. He was sensitized to D. pteronyssinus(2.58KU/L) and D. farinae(3.13KU/L) on Immuno-CAP system. Chest x-ray showed decreased left lung volume and vascularity, compared to right side. Comoputerized tomography (CT) scans demonstrated decreased lung volume, hyperlucency and hypoplastic pulmonary artery are seen in the left lung were noted. Pulmonary function test reveled severe airway obstruction with response to bronchodilator (FEV1: 46%, FEV1/FVC 54% and 20% increased in baseline FEV1). He was discharged from the hospital with inhaled corticosteroid and bronchodilator. Conclusion: SJS can be easily misdiagnosed. It is diagnosed on the basis of medical history, clinical presentation, chest x-rays and CT findings. In this case, the CT findings of small lung volume, hyperlucency and hypoplastic pulmonary artery is characteristic of SJS. It should be considered if there is a small lung volume and hypoplastic pulmonary artery on chest x-ray in patient who had pulmonary infections.