In a man aged 34 who had been experiencing frequent coughing since November 2001, a chest radiograph showed infiltration shadows in both lung fields. Chest CT showed diffuse centrilobular nodules and multiple mediastinal lymphadenopathy. Laboratory examination revealed high values for C-reactive protein and the erythrocyte sedimentation rate, together with polyclonal hyperimmunoglobulinemia and an elevated interleukin-6 level. We suspected multicentric Castleman's disease, and so performed thoracoscopic mediastinal lymph node biopsy and lung biopsy. The former disclosed follicular hyperplasia and plasma cell infiltration in the interfollicular area, suggesting a diagnosis of Castleman's disease, plasma cell type. The lung biopsy showed heavy infiltration of plasma cells. The diagnosis was therefore multicentric Castleman's disease (MCD) with pulmonary involvement. The chest CT findings were tpyical characteristics of pulmonary involvement in patients with MCD.