We reported a case of acute disseminated encephalomyelitis (ADEM) after Streptococcus infection. Brain MRI (T₂-weighted image) showed high intensity lesion in the gray matter in the acute phase. The high intensity pattern of the lesion was different from those in previously reported cases. The boy, aged 14, had fever late in August 1993. He had lumbago and back pain since September 3 and also leg weakness developed since September 7. He became unable to urinate on September 10 and was admitted on September 12. His consciousness became indistinct. We considered ADEM on the basis of high CSF level of myelin basic protein, clinical course, symptoms and MRI findings and began to administer steroid hormone on the second day after admission. He rapidly recovered. We reported here an atypical case of ADEM as to the antecedent infection and MRI lesion.