The CNS inflammatory demyelinating disorders of childhood include both self-limited and lifelong conditions, which can be indistinguishable at the time of initial presentation. Clinical, biologic, and radiographic delineation of the various monophasic and chronic childhood demyelinating disorders requires an operational classification system to facilitate prospective research studies. The National Multiple Sclerosis Society (NMSS) organized an International Pediatric MS Study Group (Study Group) composed of adult and pediatric neurologists and experts in genetics, epidemiology, neuropsychology, nursing, and immunology. The group met several times to develop consensus definitions regarding the major CNS inflammatory demyelinating disorders of children and adolescents. Clinical definitions are proposed for pediatric multiple sclerosis (MS), acute disseminated encephalomyelitis (ADEM), recurrent ADEM, multiphasic ADEM, neuromyelitis optica, and clinically isolated syndrome. These definitions are considered operational and need to be tested in future research and modified accordingly. CNS inflammatory demyelinating disorders presenting in children and adolescents can be defined and distinguished. However, prospective research is necessary to determine the validity and utility of the proposed diagnostic categories.