PURPOSE: Acute disseminated encephalomyelitis (ADEM) is an inflammatory demyelinating disease of the central nervous system. The pathogenesis is not well known, but it is thought to be an immune-mediated disease and may follow a viral infection or vaccinations. MRI demonstrates decreased signal on T1 weighting and increased signal on T2-weighted image. We report clinical features and characteristic MRI findings in seven patients with ADEM who confirmed the preceding infections serologically. METHODS: Patients admitted to the Department of Pediatrics at Asan Medical Center as having ADEM were evaluated for the preceding infections : CSF findings, MRI findings, effects of high-dose steroids and follow-up on changes of neurological symtoms and MRI findings. RESULTS: The onset of neurological symptoms from preceding infection was between 1-3 weeks. The etiologies were Epstein-Barr virus in two, mycoplasma pneumoniae in three, and measles virus in two cases. All lesions found in MRI were cerebral white matter lesions of which there were subcortical white matter in three, corpus callosum in three, deep white matter in two, periventricular white matter in one, internal capsule in one, and cerebral peduncle in one case. There were a total of 3 cases with gray matter lesions. Two cases were treated with high- dose methyl prednisolone, one which showed a good clinical response with much improved lesions on follow-up T2-weighted image, but no clinical response in the other with aggravated MRI lesions. There was 1 patient with gadolinium enhancement lesion in acute phase and the lesion was completely resolved after steroid treatment. CONCLUSION: MRI shows various features in ADEM and may be useful in diagnosis and evaluation of clinical course.