We reported a rare case of early-onset acute disseminated encephalomyelitis (ADEM). After a nonspecific upper respiratory infection, a 14-month-old boy developed oculomotor nerve paralysis, nystagmus, intention tremor and ataxic gait. MRI showed extensive symmetric high signal lesions in th bilateral cerebellar and cerebral white matters. We made the diagnosis of ADEM on the basis of high CSF myelin basic protein, clinical course, symptoms and MRI findings. Following the administration of steroid hormone, his clinical symptoms rapidly improved.