A 32-year-old woman complaining of cough, sputum, and chest discomfort for the past ten days was admitted to the hospital. The radiologic findings were transradiant left lung with reduced number and size of vessels, mediastinal shifting to the right at expiration, matched ventilation-perfusion defect on ventilation-perfusion scan, and diffuse hypoplasia of the left pulmonary artery and i1s branches on the pulmonary angiography. We describe a case of unilateral hyperlucent lung by main bronchus obstruction in a patient who presents a clinical picture suggestive of the Swyer-James syndrome.