Postinfectious forms of encephalomyelitis, also termed acute disseminated encephalomyelitis (ADEM), form one of several categories of inflammatory demyelinating disorders of the central nervous system (CNS). Recent large, retrospective case series have refined our understanding of the clinical, laboratory, and neuroimaging characteristics of ADEM. The differences between childhood and adult ADEM, risks of development of multiple sclerosis, and the contributions of recent studies to refining the nosology of CNS demyelinating syndromes are discussed.