Neuromyelitis optica (NMO) is an uncommon, demyelinating disease that causes long-term disability in adults. Though much has recently been learned about its pathogenesis, there are still only a few studies regarding the epidemiology of NMO. The aim of the study was to describe the epidemiology of NMO among adults in the Merseyside county of the United kingdom. Multiple overlapping sources of data were used including hospital records of The Walton Centre for Neurology and Neurosurgery in Liverpool, regional district general hospital data, central Aquaporin-4 antibody testing laboratory data and the British Neurological Surveillance Unit- to identify adults with a first-ever-in-a-lifetime diagnosis of NMO. As of December 31, 2010, there were eight cases (five NMO; three NMO spectrum disorder), indicating a prevalence of 7.2/million (95 % CI 3.1-14.2). Four incident cases of NMO and three incident cases of NMO spectrum disorder were identified in this period, indicating a minimum combined average annual incidence rate of 0.8/million (95 % CI 0.3-1.6). NMO still remains an uncommon condition, but the prevalence is rising with early diagnosis.