The authors report on 3 cases of malignant lymphoma associated with well-defined lytic lesions of the skull and limbs that were identical to lesions observed in patients with multiple myeloma. In two patients, subcutaneous nodules were found opposite the site of bone lysis. Histologic examination diagnosed centrofollicular cell malignant lymphoma in all 3 cases. The exceptional nature of such lesions in patients with malignant lymphoma is discussed in connection with literature data. The suggested physiopathologic mechanism is secretion of an "osteoclast activation factor" (OAF) by malignant lymphoid B cells.