We report a case of acute disseminated encephalomyelitis preceding measles virus infection. Brain magnetic resonance imaging revealed signal intensity abnormalities in the basal ganglia and cortex consistent with acute disseminated encephalomyelitis. Fever and the first Koplik spots appeared 8 and 10 days later, respectively. This case supports the hypothesis that the immune-mediated demyelinating process may occur before the symptomatic phase of a viral infection. Therefore, children without history of infectious disorders should also have acute disseminated encephalomyelitis included in the differential considerations.