Abstract Multiple sclerosis (MS) is the most important autoimmune disease of the central nervous system (CNS). Its animal model experimental autoimmune encephalomyelitis (EAE) has been instrumental in defining the features of the novel T helper cell subset Th17. Conversely, the broad characterization of Th17 immune responses has substantially advanced our understanding of organ-specific autoimmunity and inspired almost a decade of immunological research. Here, we review the current knowledge on Th17 cells and their contribution to the immunopathology in EAE and MS, covering recent proceedings in the induction, modulation and effector mechanisms of this versatile T lymphocyte subset. In particular, we discuss the emerging role of mucosal immunity in the regulation of Th17 cells and CNS autoimmunity, the accumulating evidence for extensive plasticity in the Th17 subset, and their molecular mode of action in promoting this debilitating disease.