An 80-year-old female patient arrived with a pronounced lymphadenopathy and weight loss. 6 years ago she had been diagnosed with rheumatoid arthritis. At the time of arrival, she was administered Methotrexate (MTX) 10 mg/week.
 By lymph node biopsy, a clonal population of both EBV-positive B and T cells was seen. Newly occurring anemia (Hb 10 g/dl), monoclonal gammopathy of the Ig M isotype and detection of 40 % EBV-positive plasma cells in the bone marrow were consistent with the diagnosis of Ig M myeloma. We interpret these findings as a biclonal Epstein Barr Virus-positive Methotrexate-associated lymphoproliferative disorder (MTX-LPD).
 The clinical condition improved immediately after MTX discontinuation. In the follow-up after 4 months, the gamma globulin concentration in serum was significantly reduced (from 51.1 to 34.7 %) and a renewed immune electrophoresis of the serum was without evidence of monoclonal gammopathy.
 Based on this case, the association of RA with lymphoproliferative disorders can be confirmed – here as an association of RA with biclonal MTX-LPD or multiple myeloma. Therapy with MTX and reactivation of EBV infection are important influencing factors.