An 18-year-old female had common cold and insomnia in early March 1987. Later, abnormal speech and behavior, emotional incontinence, anorexia and consciousness disturbance appeared. On March 19, she was admitted to our hospital in semi-comatose state. Myoclonus-like movement on hands was observed, and epileptic attacks with tonic and clonic convulsions occasionally occurred. There were no neurological findings that suspected cerebral focal lesions. The respiration was assisted through tracheal intubation. Laboratory examinations showed inflammatory reactions (CRP+2, WBC 10,600) and transient high levels serum CK (6,215 IU). As she had bradycardia (30-40/min) with complete AV block on ECG, the pacemaker was implanted. The complication of myocarditis was suspected. EEG showed bilateral slow waves (3-6Hz), dominantly in frontal areas. Brain CT and CSF examinations were normal. After the combined administration of ara-A, dexamethasone and anti-convulsant, the consciousness level was recovered within a month. The serum antibody against coxsackie virus B4 alone was significantly increased. We concluded that coxsackie virus B4 caused acute encephalitis with mental symptoms and myocarditis with AV block. Recently, cytomegalovirus was reported to be the causative virus in a young female with non-HSV encephalitis who showed mental symptoms with good prognosis, but coxsackie virus B4 should also be considered as one of the causative viruses.