Optic neuritis (ON) is an autoimmune acute demyelinating disease of the optic nerve and may occur in patients with confirmed multiple sclerosis (MS) or as a clinically isolated syndrome. T lymphocytes play a central role in the pathogenesis of MS. The phenotype of different T cell subsets is usually characterized by the expression of distinct cell surface receptors such as CD45RA, CD45RO, CCR7, CD27 and CD28. The aim of this study was to characterize the phenotype of distinct subsets of CD4 and CD8 T cells in patients with isolated ON.