Neuromyelitis optica is a rare variant of multiple sclerosis which tends to be more severe and particularly affects vision and walking. Recently an unusual antibody to a water channel molecule (aquaporin-4) has been described in association with this condition supporting the long held clinical view that it may be a separate disease or is at least a distinct variant of multiple sclerosis. However, because of overlap in clinical features and a lack of precision in testing for this antibody considerable doubt remains regarding both the status of neurolmyelitis optica as a separate entity and the role of the aquaporin-4 antibody plays in diagnosis. Through a combination of extensive population-based collection of clinical data and systematic testing with MRI and antibodies this study hopes to clearly define the true spectrum of this disease and the value of aquaporin-4 antibodies play in diagnosis. The study will involve a nationwide survey of neuromyelitis optica in Australia and New Zealand and will provide accurate data on the sensitivity and specificity of various components of the diagnostic criteria including the aquaporin-4 antibody test. It is hoped that this study will advance our knowledge of how to diagnose this condition and shed light upon its cause. It is also hoped that the study will provide a platform for future study including clinical trials to improve the treatment of this condition.