A 31-year-old woman was admitted to our hospital because of progressive dyspnea and chest X-ray abnormality. She was given a diagnosis of bronchial asthma 3 years previously. She had received medical treatment, but her dyspnea did not improve. Chest CT showed multiple thin-walled cysts and centrilobular nodules throughout both lungs. Video-assisted thoracoscopic lung biopsy revealed remarkable plasmacytic infiltration in the bronchioles and its surrounding interstitium. Small cystic lesions were detected and with remarkable mural plasmacytic infiltration. The immunohistochemistry showed infiltrated plasmacytes with polyconal characteristics. Her biochemical examinations showed polyclonal hyperimmunoglobulinemia and a high range of serum IL-6. In addition, CT scans showed multiple mediastinal and intraperitoneal lymphadenopathy. From these examinations, she was given a diagnosis of multicentric Castleman disease (MCD) with pulmonary involvement showing diffuse cystic change. This case showed an unusual pattern of MCD with pulmonary involvement. However, we suggest that MCD also should be considered as a differential diagnosis in cases with diffuse lung cystic changes.