Neuromyelitis optica (NMO) was first described as a severe monophasic syndrome of acute bilateral optic neuritis and transverse myelitis. Whether it is a form of multiple sclerosis (MS) or a separate disease entity has been continually debated since the beginning of last century. The redefinition of NMO as a relapsing disease, the wider use of magnetic resonance imaging showing longer spinal cord lesion, and the recently discovered anti-aquaporin-4 (AQP4) water channel antibody, or NMO-IgG, has rekindled this controversy. The many recent publications including the abstracts published in this issue of Neurology Asia have shown that anti-AQP4 antibody is of variable sensitivity in different populations. It appears to be associated mainly with longitudinal extensive spinal cord lesions and frequent relapses. The site of pathology of NMO also do not co-localize with the widespread expression of AQP4 in the body, throwing doubts on the suggestion that the anti-AQP4 antibody plays primary role in the pathogenesis of NMO. In the day-to-day clinical practice in Asia, anti-AQP4 antibody remains a research investigatory test. As for optic-spinal MS, which is closely similar to NMO based on recently revised criteria, interferon should remain the treatment of first choice.