We describe the case of a 36-year-old woman who developed acute encephalo-myelitis after acute viral hepatitis type B. She was admitted to the hospital with a history of general malaise and nausea of 5 days duration. Her serum showed high transaminase levels and positive HBs-Ag and increased IgM HBc-Ab titers. She had urinary dysfunction, myoclonus and postural tremor of her extremities. Several days later, she developed bilateral limb ataxia and alteration of consciousness. The cerebrospinal fluid examinations showed pleocytosis and increased protein. Treatment with high-dose methylprednisolone resulted in a marked improvement of the clinical and CSF examination. Magnetic resonance imaging of the brain and the spinal cord did not disclose abnormal lesions. The symptoms and clinical course were quite similar to those of acute disseminated encephalomyelitis.