A 75-year-old woman was referred to us because of cough, high fever and skin erythema in April 1999. Malignant lymphoma (diffuse mixed cell type) was previously diagnosed in 1990 and she achieved complete remission after treatment with a series of CHOP regimen treatments. In 1998, multiple myeloma (IgG lambda type) was diagnosed and she was treated with a combination of melphalan and prednisolone. On physical examination, superficial lymphadenopathy and skin erythema were noted. Biclonal gammopathy (IgG kappa/lambda) was shown in serum, and Bence Jones protein in urine. Computed tomography showed pleural effusion and swelling of paraaortic lymph nodes. The bone marrow examination showed an increased number of abnormal plasma cells (19.2%) and no evidence of lymphoma. Left axillary lymph node biopsy revealed that she had non-Hodgkin's lymphoma (immunoblastic lymphadenopathy-like T cell lymphoma). She was treated with the CHOP regimen at reduced doses for both diseases. The lymphoadenopathy reduced after 6 courses of CHOP and 4 courses of CHOPE (CHOP + VP16), however, she had bone pain on November 1999 and received treatment with MCNU-VMP (MCNU + VDS + L-PAM + PSL). Her rib pain improved, but she died of systemic infection of herpes zoster virus. We report here a rare case of malignant lymphoma concomitant with multiple myeloma.