Transverse myelitis (TM) is the prototype inflammatory myelopathy. TM is a clinical syndrome in which an immune-mediated process causes neural injury to the spinal cord, resulting in varying degrees of weakness, sensory alterations, and autonomic dysfunction. TM may exist as part of a multifocal central nervous system disease (eg, multiple sclerosis), multisystemic disease (eg, systemic lupus erythematosus), or as an isolated, idiopathic entity. With more rigorous criteria applied to distinguish acute myelopathies and with an emerging understanding of immunopathogenic events that underlie TM, it may now be possible to initiate effective treatments in many of these disorders. The investigation of TM results in a broader appreciation of the mechanisms that lead to autoimmune neurological diseases in general.