The clinical and pathological characteristics of acute disseminated encephalomyelitis are briefly outlined. The possible relation between acute disseminated encephalomyelitis and other isolated monophasic inflammatory demyelinating episodes in the central nervous system, such as acute optic neuritis, transverse myelitis or brainstem lesions, is noted and the risk of progression to multiple sclerosis is examined. The surprising results of a clinical trial of corticosteroids in optic neuritis are of particular interest in this regard, and we speculate on an explanation in terms of a spread of antimyelin T cell receptor gene usage over time. Finally, the risk factors for the progression of demyelinating ther than optic neuritis to multiple sclerosis are explored. Further work to elucidate better the relationships between these pathological entities is suggested.