Methotrexate-related lymphoproliferative disorder (MTX-LPD) is a rare disorder caused by long-term MTX therapy for autoimmune diseases. There has been no report of the dermoscopic features of MTX-LPD to date. A 64-year-old female presented with a slightly elevated indurated erythematous plaque with scales on her right thigh. The patient had been treated for rheumatic arthritis with MTX and prednisolone for more than 15 years, and 18 mg/week MTX without prednisolone had been administered in the last year. Dermoscopy revealed dotted vessels and glomerular vessels on pink homogeneous areas and multiple surface scales. Enhanced computed tomography showed multiple nodules and lymphadenopathies at the mediastinum and axillae. Histopathological examination revealed telangiectasia in the superficial dermis. Atypical lymphoid cells were scattered in the whole dermis and subcutaneous tissue. A perivascular infiltrate of atypical lymphocytes and histiocytoid cells partially destroyed the vessel walls. Epstein-Barr virus in situ hybridization showed a positive result. The cessation of MTX reduced the erythematous plaque, and lymphadenopathies at the neck, mediastinum, and axillae were not palpable. We discuss the relevance of these dermoscopic and histopathological features. The accumulation of such cases will reveal the dermoscopic features of MTX-LPD and the utility of dermoscopy for the diagnosis of MTX-LPD.