Methotrexate (MTX) is an established immunomodulating agent used in low doses (LDMTX) to treat several autoimmune diseases. Ulcerative stomatitis (US) may be observed as a long-term LDMTX adverse effect showing a wide histopathologic spectrum. A 73-year old female presented with painful oral ulcers of 5 days duration. The patient had been under treatment for rheumatoid arthritis with LDMTX, while one week before presentation she was prescribed ciprofloxacin for a urinary infection. Histopathologic examination of a lingual ulcer revealed a polymorphous lymphohistiocytic proliferation with scattered binucleated atypical lymphocytes. Immunohistochemically, most cells were of T-cell lineage while the EBER test was negative and a diagnosis of MTX-induced reactive ulceration was rendered. MTX cessation resulted in complete resolution of the ulcers with no recurrences reported so far. The clinical and histopathologic features of MTX-induced oral ulcers are not always diagnostic and a detailed history and an extensive clinicopathologic investigation may be needed to exclude a lymphoproliferative disorder.