Reliable biomarkers corresponding to disease progression or therapeutic responsiveness in multiple sclerosis (MS) have not been yet identified. We previously reported that low expression of the antiproliferative gene TOB1 in CD4⁺ T cells of individuals presenting with an initial central nervous system (CNS) demyelinating event (a clinically isolated syndrome), correlated with high risk for progression to MS. We report that experimental autoimmune encephalomyelitis (EAE) in Tob1⁻/ ⁻ mice was associated with augmented CNS inflammation, increased infiltrating CD4⁺ and CD8⁺ T cell counts, and increased myelin-reactive Th1 and Th17 cells, with reduced numbers of regulatory T cells. Reconstitution of Rag1⁻/ ⁻mice with Tob1⁻/⁻ CD4⁺ T cells recapitulated the aggressive EAE phenotype observed in Tob1⁻/⁻ mice. Furthermore, severe spontaneous EAE was observed when Tob1⁻/⁻ mice were crossed to myelin oligodendrocyte glycoprotein–specific T cell receptor transgenic (2D2) mice. Collectively, our results reveal a critical role for Tob1 in adaptive T cell immune responses that drive development of EAE, thus providing support for the development of Tob1 as a biomarker for demyelinating disease activity.