A 69-year-old man with blastic natural killer cell lymphoma (BNKL) was treated mainly with methotrexate (MTX). He presented with skin and bone marrow involvement at onset. Neoplastic cells were blastic in appearance with CD3−, CD4−, CD8−, CD7−, CD16−, CD56+ and HLA-DR+ phenotype. Molecular studies showed germline configuration of both immunoglobulin H and T cell receptor genes, and negative results for Epstein–Barr virus-encoded small RNA (EBER). He was treated with standard acute lymphoblastic leukemia (ALL) induction therapy, followed by 1 cycle of high-dose MTX (HD-MTX) as consolidation therapy. However, BNKL relapsed during standard ALL maintenance therapy. Three cycles of HD-MTX were effective in achieving a second complete remission and then he received low dose MTX as maintenance therapy. BNKL remained well controlled for 4 years. Chemotherapeutic toxicity was mild and manageable. Since BNKL reportedly has a poor prognosis, this encouraging result warrants further investigation of MTX as either a single agent or in a combination regimen as a first-line treatment for patients with BNKL.