A 66-year-old woman was referred to our hospital for cough and dyspnea in November 2008. Chest CT scan showed multiple infiltration shadows in the left lower lobe and right middle and lower lobes of the lungs. We administered antibiotics as community-acquired pneumonia, but her symptoms were not improved, and exacerbation of alveolar opacities was demonstrated. We suspected cryptogenic organizing pneumonia (COP) and performed a transbronchial lung biopsy (TBLB). However, the biopsy specimens revealed noncaseating granulomas, and we diagnosed as pulmonary sarcoidosis. PAB antibody positive cells were also detected in the granulomas. Subsequently, alveolar opacities became worse, but oral corticosteroid therapy improved her symptoms and the X-ray findings. Battesti et al. reported alveolar sarcoidosis with an acute course and good response to corticosteroids. We concluded that this case was consistent with their report.