OBJECTIVE Acute disseminated encephalomyelitis (ADEM) is a monophasic demyelination disease of central nervous system (CNS) with presentations of impaired consciousness, neurologic deficits and diffuse white matter lesions on magnetic resonance imaging (MRI). Predisposing infection can be identified in around 50 to 77% of all patients with ADEM. Post-infectious autoimmune events associated with Japanese encephalitis have been limited to case reports of Guillain-Barre syndrome after Japanese encephalitis and Japanese encephalitis virus vaccine-related ADEM. We herein report the first possible patient with Japanese encephalitis developed a subsequent ADEM after recovery from Japanese encephalitis. METHODS A 50-year-old man suffered from an acute onset of headache, fever, and disturbance of consciousness. Japanese encephalitis was diagnosed by virological and image study. He recovered gradually and was discharged about 1.5 months later. However, another episode of consciousness impairment with violent behavior occurred 21 days after discharge. Acute disseminated encephalomyelitis was confirmed by brain MRI which showed newly developed diffuse white matter lesions. His clinical symptoms and abnormal brain lesions on MRI improved gradually after combination of high-dose intravenous methylprednisolone and oral steroid therapy. CONCLUSIONS Our patient is a possible case of ADEM developing after Japanese encephalitis. High dose steroid therapy resulted in good outcome of ADEM.