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