An adult female white-tailed deer (Odocoileus virginianus) with a history of shaking, ataxia, and severe debilitation was submitted for examination. Macroscopic lesions included severe emaciation, severe abdominal and mesenteric lymphadenopathy, and several rumen-associated masses. Microscopically, the ruminal masses and lymph nodes were infiltrated by pleomorphic neoplastic lymphocytes. Similar lymphoblasts were associated with the leptomeninges, choroid plexus, and the intestinal mucosa; these cells were intensely positive for CD3 antigen, indicating their T-cell origin. Lymphoproliferative viruses (bovine leukemia virus and malignant catarrhal fever virus) or epizootic hemorrhagic disease virus were not detected by polymerase chain reaction. To our knowledge, this case represents the first report of the immunophenotype of a multicentric lymphosarcoma, metastasis involving the brain, and epitheliotropic lymphoblasts in a white-tailed deer.