We report a rare case of primary central nervous system (CNS) lymphoma as methotrexate-associated lymphoproliferative disorders (MTX-LPD). A 75-year-old woman who had been treated for rheumatoid arthritis (RA) with MTX for 3 years was admitted to our hospital complaining of unsteady gait, nausea, and vomiting. T2-weighted image of magnetic resonance imaging (MRI) showed multiple high intensity mass-like lesions including right lateral, frontal and temporal lobes, and right cerebellar hemisphere. We performed surgical biopsy, and the pathological and immunohistochemical examinations identified T-cell lymphoma. The tumor regressed and the symptoms were resolved soon after MTX withdrawal. Primary CNS lymphoma due to MTX-LPD is a rare disease and only eight cases including ours are reported.