Neuromyelitis optica spectrum disorder (NMOSD) is a group of rare and mostly severe autoimmune demyelinating central nervous system disorders which prevalence is 0.7—1 per 100.000 population and incidence is 0.037—0.73 per 100.000 person-years. NMOSD may present as a combination of uni- or bilateral optic neuritis, transverse myelitis or lesions of brain stem and other brain regions. The symptoms are mostly relapsing (up to 97.5%) and progressive. Occurrence of relapses is associated with seropositivity for aquaporin-4 (up to 80% of NMOSD patients) and bears a less favorable prognosis (mortality up to 32%). Women seropositive for aquaporin 4 constitute 90% of NMOSD patients. Compared to other demyelinating disorders, NMOSD is characterized by late onset (mean age is about 39 years) and association with other autoimmune disorders, including systemic lupus erythematosus, myasthenia gravis and Sjogren’s syndrome. A genetic predisposition was found among Blacks and Asians, with HLA-DRB1*03:01 gene associated with higher risk of NMOSD in Asians. The course of the disease tends to be more severe in Blacks. There are clusters of an increased incidence of NMOSD in the Carribeans and in the Far East. Continued increase of prevalence and incidence of NMOSD worldwide compels continued epidemiological research in order to provide early diagnosis and treatment for this disorder.