Pulmonary alveolar proteinosis (PAP) is a rare disease with an unclear etiology, in which the alveoli became filled with a periodic acid-Schiff (PAS)-positive proteinaceous material. We present the case of a 32-year old man with prominent symptoms of dry cough and progessively dyspnea for two weeks. Routine chest radiography showed diffuse interstitial and alveolar opacity of both lungs. High resolution computed tomography (HRCT) revealed diffuse bilateral ground-glass opacity, areas of air-space consolidation, and thickened interstitial septa. These findings were very suggestive of the diagnosis of PAP. Open lung biopsy was performed providing pathologic confirmation of PAP. The clinical course and HRCT features of this patient are discussed.