Pulmonary alveolar proteinosis is a disease of unknown etiology characterized by the accumulation of PAS positive lipoproteinaceous material in the alveolar spaces sparing septum The therapy which has enjoyed the greatest success is whole lung lavage. The authors reported here, a case of 44 year old male patient with pulmonary alveolar proteinosis, and this is the 7th case in Korea. The patient underwent whole lung lavage but expired due to brain edema complicated by the procedure. He complained exertional dyspnea and cyanotic lips, and presented fine inspiratory crackle at both lower lung fields, decreased arterial oxygen pressure, and diffuse infiltration at whole lung field. Light microscopic finding of lung tissue obtained by transbronchial lung biopsy revealed PAS positive amorphous, granular material filled in the alveolar spaces, and electron microscopy of bronchoalveolar lavage fluid concentrate showed many electron-dense multi-lamellated structures. To treat the disease, the authors tried whole lung lavage of left lung with 37℃ isotonic saline under general anesthesia. However, he expired due to brain edema probably due to dilutional hyponatremia complicated by the procedure, 11 days after the procedure. Whole lung lavage is known relatively safe, but fatal complication may occur like this case.