Neuromyelitis optica (NMO) is a severe, inflammatory, demyelinating disorder characterized by recurrent attacks of optic neuritis or longitudinally extensive transverse myelitis which may occur either simultaneously sequantially, or in isolation. NMO astrocytic water channel aquaporin-4 (AQP4)-IgG selectively binds to the abluminal face of central nervous system (CNS) microvessels, and colocalizes with the extracellular matrix protein laminin and subpia in a distribution that paralleled the immunocomplex deposition. Detailed immunopathologic evaluation of autopsied and biopsied CNS tissues from patients with NMO or NMO spectrum has shown significant difference when compared with multiple sclerosis (MS). Patients with NMO spectrum disorders commonly have coexisting non-organ-specific auto antibodies and multisystem autoimmune diseases. In NMO, attacks of optic neuritis or transverse myelitis are frequently severe. Acute optic neuritis is often associated with significant loss of vision. Mycophenolate mofetil is a reasonably safe medication and appears to be effective in the prevention of NMO relapse.