In 1998, a 68-year-old woman was diagnosed with rheumatoid arthritis. She was treated with prednisolone, nonsteroidal anti-inflammatory drugs, methotrexate (MTX), and biological drugs. Retroperitoneal lymph node swelling and hepatosplenomegaly appeared but spontaneously disappeared after drug withdrawal. Anorexia and general fatigue occurred in March 2012. She was admitted to our hospital with retroperitoneal, periaortic, and mediastinal lymph node swelling and was found to have multiple liver tumors. Based on the results of aspiration biopsy of a liver tumor, she was diagnosed with malignant lymphoma (Hodgkin lymphoma). She died from liver failure and disseminated intravascular coagulation before chemotherapy. We present this case of MTX-associated lymphoproliferative disorder, which caused formation of a liver tumor.