A 6-year-old girl (Patient 1) and a 5-year-old boy (Patient 2) with acute disseminated encephalomyelitis after Japanese B encephalitis vaccination are reported. Drowsiness, paresthesias, and gait disturbance were observed at 14 days (Patient 1) and 17 days (Patient 2) after the vaccination; however, transient impairment of visual acuity was only found in Patient 1. Laboratory examinations revealed slow theta waves on electroencephalography and elevated myelin basic protein in the cerebrospinal fluid in both patients. The most striking feature on magnetic resonance imaging was the combination of white matter lesions and abnormal intensity signals of the thalamus. The administration of oral prednisolone (2 mg/kg/day) markedly improved the clinical findings and abnormal magnetic resonance imaging findings. A similar magnetic resonance imaging finding of abnormal intensity of the thalamus with deep white matter lesions has been reported in patients with Japanese B encephalitis; therefore, thalamic lesions may be related to the naturally occurring encephalitis.