PURPOSE: Acute disseminated encephalomyelitis (ADEM) is a demyelinating disease of the central nervous system preceded by viral illnesses or vaccinations. Diagnosis depends on the clinical manifestations and the neuroimaging findings. The authors analyzed the clinical differences according to the extent and distribution of lesions on brain MRI. METHODS: We studied 24 ADEM patients diagnosed by clinical and radiologic findings from 1990 to 1999. We classified the MRI findings as follows. W group : Multifocal lesions only in the white matter; G group : Lesions in the deep gray matter with or without in the white matter. Neurologic findings, clinical courses, outcomes were compared between the 2 groups. RESULTS: Nine of 12 (75%) and 7 of 12 (58%) had altered mentality in W group and G group respectively. Five of 12 (42%) and 3 of 12 (25%) had seizures in W group and G group respectively. Other neurological manifestations were as follows : Pyramidal tract signs, motor disturbances, facial palsy and ataxia. Ten of 12 (83%) and 11 of 12 (92%) showed clinical improvement in W group and G group respectively. Median recovery times were 29 days in W group and 24 days in G group. Seven of 12 and 9 of 12 were recovered completely without neurological sequelae. CONCLUSION: Although there was no statistically significant difference, ADEM may be a group of heterogeneous disorders, since the clinical and radiological manifestations are quite diverse. Caution should be made on the MRI distribution of lesions need to be considered in the diagnosis of the patients who are suspected as having ADEM.