Methotrexate-associated lymphoproliferative disorder (MTX-LPD) is a lymphoid proliferation or lymphoma in an immunosuppressed patient administered with MTX. Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a clinical condition characterized by bone exposure in the oromaxillofacial region of the patients administered with BPs. Here, we report a case of MTX-LPD complicated by BRONJ occurred in a 67-year-old Japanese woman with RA, who received MTX and alendronate sodium hydrate for several years. She had a mass with ulcer formation in the area of hard palate. Histopathologically, large atypical lymphoid cells were found to infiltrate into granulation tissue in the ulcerative oral mucosa. Immunohistochemistry showed that the large atypical lymphoid cells were positive for Ki-67, CD3, CD30, and CD79a and negative for CD15, ALK1, and AE1/AE3. Withdrawal of MTX therapy led to complete remission within 4 weeks. However, 9 weeks later, necrotic bone was formed on hard palate and sequestrectomy was performed twice. Thereafter, the operation for closing naso-oral fistula was performed. The patient has been free of recurrence for 1 year since fistula closure. This is a very rare case in which the oral cavity was the initial site of manifestation of MTX-LPD followed by BRONJ in the patient with RA. © 2014 Asian AOMS, ASOMP, JSOP, JSOMS, JSOM, and JAMI.