Inflammatory demyelinating diseases comprise a series of autoimmune disorders affecting myelin at the level of the central nervous system (CNS) and peripheral nervous system. They can be monophasic, multiphasic, progressive, monofocal or multifocal, and their diagnosis is usually of exclusion. We report the case of a 15-year-old female patient with headache, ataxia, hemiparesis, ophthalmoplegia and altered consciousness. Magnetic resonance imaging showed lesions compatible with demyelinating disease. Acute disseminated encephalomyelitis was diagnosed. The patient responded to treatment with corticosteroids.