Methotrexate-associated lymphoproliferative disorder (MTX-LPD) can occur in the oral cavity, and only a few cases with palatal involvement have been reported. Chemotherapy may be needed if there is no remission after the withdrawal of MTX. We report a case of MTX-LPD presenting with a swelling of the palate that required chemotherapy. A woman in her 70s with rheumatoid arthritis reported a swelling on the left side of the palate. Her condition was diagnosed as Epstein-Barr virus-negative diffuse large B-cell lymphoma (MTX-LPD). Since the mass did not remit after MTX withdrawal, she underwent five courses of chemotherapy. Currently, the patient is in complete remission. In patients on MTX who develop a swelling on the palate, MTX-LPD should be included among the differential diagnostic possibilities. Diagnosis and treatment of MTX-LPD call for consultation with a haematologist. If the mass fails to regress following withdrawal of MTX, appropriate chemotherapy is indicated.