: We report a case of histopathologically-confirmed primary central nervous system lymphoma who was initially diagnosed as demyelinating encephalopathy. A 58-year-old woman was admitted with confusion and left hemiparesis. Head MR showed abnormal flaky hypointense T1 and hyperintense T2 signals at right thalamus, splenium of corpus callosum, bilateral cerebral peduncle, pons, medulla oblongata, basal ganglia and right corona radiata. Her mental status improved a little and she was discharged from hospital after neuroprotective treatment. 10 days after her discharge, her confusion appeared again with hallucination and unsteady walking. Pathological examination revealed non-Hodgkin's lymphoma (WHO classification: DLBCL). The patient continued to deteriorate after the surgery and died 10 days later.