A 5-year-old intact male Persian cat was presented with progressive neurologic deficits, hyperesthesia, hyperreflexia, ataxia, and intention tremors, which resulted in death. Serologic tests for feline leukemia virus and feline immunodeficiency virus infection were negative. Neurohistologic examination revealed the presence of pleomorphic cellular infiltrates in cerebral leptomeninges and around parenchymal vessels. The majority of infiltrating cells were uniformly immunostained using an antiserum directed against T cells. Immunohistochemical examination of paraffin-embedded brain sections for the antigens of canine distemper virus, herpesvirus, Borna virus, and Toxoplasma gondii were negative. Histologic and immunohistochemical studies revealed a primary central nervous system T-cell lymphoma affecting the brain.