Although Castleman disease may occur in any lymph node of the body, it is the most commonly found in the thoracic cavity. Castleman disease rarely occurs in the pelvic cavity and only 8 such cases have been reported previously in Japan. In this report, we describe a case of Castleman disease in the pelvic cavity. A 36-year-old man complained of fever. Both serum c-reactive protein (CRP) and serum interleukin-6 (IL-6) were elevated. Computed tomography and magnetic resonance imaging showed a solid mass with calcification in the pelvic cavity. The pelvic mass was surgically excised. The removed mass was solid and 75 x 45 x 30 mm in size. The histological diagnosis was the plasma cell type of Castleman disease. Fever subsided and both serum CRP and serum IL-6 were normalized after the operation. No evidence of disease was detected one year post operation.