Neuromyelitis optica (NMO) is currently recognized as a broad spectrum of autoimmune disorders of the Central Nervous System (CNS), causing demyelinating and inflammatory injuries, primarily in the spinal cord and optic nerves, but also in other regions such as brainstem, diencephalon or specific brain areas. These disorders are grouped under the unifying term "NMO spectrum disorders" (NMOSD). For many years this pathological entity was thought like a variant of the Multiple Sclerosis (MS). However, current evidence shows that there are distinctive features of clinical presentation, pathophysiology, laboratory, neuroimaging and therapy response that distinguish NMOSD from the latter. Most patients with NMOSD are seropositive for autoantibodies (AQP4-IgG) against AQP4, the major water channel of astrocytes. New advances in research have allowed recognize that AQP4-IgG is pathogenic in NMOSD, probably by a mechanism involving complement dependent cellular cytotoxicity. Due to the severity of attacks in NMOSD and the high risk for neurological disability, treatment should be initiated as soon as the diagnosis is confirmed. Acute attacks of optic neuritis or myelitis are treated with high-dose intravenous corticosteroid and plasmapheresis. Maintenance therapy to avoid further relapses is based on low-dose oral corticosteroid and non-specific immunosuppressant drugs; nevertheless, to date there are no controlled randomized trials to confirm the safety and efficacy for the drugs currently used.