Anaplastic myeloma represents a rare variety of multiple myeloma, with poor prognosis and no response to therapy. 56 cases reported in the literature are reviewed and one case evaluated with immunohistochemical techniques is described. This case is of special interest in the following points: the anaplastic myeloma arose in extramedullary sites in a patient with typical multiple myeloma in remission; differential histological diagnosis between anaplastic myeloma and immunoblastic lymphoma was very difficult without immunohistochemical techniques; the anaplastic phase presented an atypical neurologic feature, the Collet-Sicard syndrome, and the treatment with radio-chemotherapy (including adriamycin) did not induce any clinical improvement.