The authors report the case of a 35 year-old polynesian male admitted to hospital with a diagnosis of myeloma. Bone marrow study showed an intense plasmocytosis, mature, Marshalko type. A new physical examination disclosed polyadenopathies and the lymph node biopsy showed lymph node modifications typical of plasma cell type Castleman's disease. At the same time, the polytypic profile of the bone marrow plasmacytosis and of the hypergammaglobulinemia was demonstrated, thus confirming the reactive state of the plasmacytosis, due to Castleman's disease. Such massive, reactive plasmacytosis belong to one of the various pathological features of multicentric Castleman's disease. Thus, this disease should belong to the etiologic diagnosis of intense bone marrow plasmacytosis and be distinguished from multiple myeloma, sometimes associated to Castleman's disease, especially in case of POEMS syndrome.