Primary non-Hodgkin's lymphoma of bone (PLB) is rare, and generally presents as a single extensive and destructive bone lesion. Histopathologically, most cases present as diffuse large B-cell lymphoma, and T-cell lymphoma is rare. By contrast, multiple myeloma is a disease defined as the neoplastic proliferation of a single clone of plasma cells producing a monoclonal immunoglobulin. We report a case of multiple myeloma that developed during treatment of PLB in a type of T-cell. A 48-yr-old man was diagnosed as T-cell PLB, stage IE, 18 months ago. The patient received the chemoradiotherapy and salvage chemotherapy for PLB. However, the lymphoma progressed with generalized bone pain, and laboratory findings showed bicytopenia and acute renal failure. On bone marrow biopsy, the patient was diagnosed as having multiple myeloma newly developed with primary T-cell lymphoma of bone. In spite of chemotherapy, the patient died of renal failure.