A 51-year-old woman presented with cough, fever, and increased serum ACE activity. Computed tomography (CT) revealed a bilateral diffuse pattern of ground-glass opacities with enlarged bilateral hilar/mediastinal lymph nodes. Sarcoidosis was diagnosed by transbronchial lung biopsy in August 2005. After treatment with 30 mg/day prednisolone, her symptoms and chest CT findings improved markedly, and her serum ACE activity also decreased. Although her symptoms had been stable, and ACE activity had been at a normal level on treatment with 10 mg/day prednisolone, multiple cystic lesions, which were not observed in May 2007, appeared in bilateral peripheral lung lesions on CT in January 2008, and progressed rapidly. We present an interesting case of pulmonary sarcoidosis, with rapid progression of multiple cystic lesions without enlargement of hilar/mediastinal lymph nodes and increased serum ACE activity on treatment with prednisolone.