We report a case of pulmonary alveolar proteinosis (PAP). A 39-year-old asymptomatic woman was admitted to our hospital because of abnormal shadows on chest X-ray films. Chest X-ray films revealed peripheral infiltrates in both lungs. Computed tomographic examination showed patchy peripheral ground-glass attenuation, concentrated subpleurally. Bronchoalveolar lavage fluid was clear. Because transbronchial lung biopsy findings were inconclusive, a VATS-biopsy was performed. The specimens demonstrated accumulation of proteinaceous materials within alveolar spaces. The patient was given a diagnosis of PAP. Although the distribution of radiographic shadows varies in patients with PAP, perihilar or centralized shadows usually predominate. In our patient, subpleural areas of the lung were affected almost exclusively.