We present here seven cases of idiopathic multicentric Castleman's disease (MCD) showing effusion at the initial clinical presentation. This series includes a high proportion of middle-aged and elderly females (5/7). Various autoantibodies were detected in six cases. Anemia (Hb < 10 g/dl) was detected in four cases, leukocytosis (WBC > 10 × 10(9)/l) in three and thrombycytopenia (<100 × 10(9)/l) in five. Positivity for C-reactive protein or elevated erythrocyte sedimentation rate was recorded in all seven cases. Elevated serum IgG level (>2000 mg/dl) was recorded in only three cases. Elevated serum interleukin-6 level was recorded in all four cases examined. At the onset of disease, four cases were associated with idiopathic thrombocytic purpura. During the course of disease, one case each was diagnosed as systemic sclerosis + Sjögren's syndrome (SJS) and SJS. Histologically, five lesions exhibited a mixed type of Castleman's disease, and one case each exhibited a hyaline-vascular type and plasma cell type. The non-neoplastic nature of the B-lymphocytes was demonstrated by immunohistochemistry and polymerase chain reaction. There were no human herpes type-8 virus-positive cells in any of the seven lesions. Good responsiveness to glucocorticoid therapy has been seen in all six cases treated. From a therapeutic perspective, it is important to discriminate this subtype of MCD.