Neuromyelitis optica (NMO) or Devic′s disease was until recently regarded as an unusual or severe variant of multiple sclerosis. However the last decade has seen major advances in our understanding of the etiopathogenesis of NMO. Though unsettled, there seems to be increasing evidence that NMO is a distinct immune mediated, largely relapsing, inflammatory, demyelinating disease of the central nervous system that most commonly targets the optic nerves and spinal cord. Longitudinally extensive spinal cord lesions on MRI, a serum antibody (NMO-IgG) which reacts specifically with water channel aquaporin 4 (AQP-4), response to immunosuppressive therapies (rather than immunomodulation like in MS) seem to be distinguish it from MS. We review the evolving epidemiological, clinical, imaging and immunological features of NMO and discuss the therapeutic options available. We also review the longstanding debate on whether NMO and Asian optico-spinal multiple sclerosis are two distinct entities or one. We have reviewed the all the published literature on NMO from India and there seems to be a higher proportion of NMO in India than reported in the West. An early accurate diagnosis and treatment with widely available drugs could alter the prognosis of NMO. A fuller understanding NMO may be the doorway to insights into MS and other demyelinating disorders. The information presented in this review has been obtained from peer reviewed publications, conference abstracts and personal experience. The data on Indian patients has been obtained by a literature search using the national library of medicine search engine with the search terms: "neuromyelitis optica or multiple sclerosis or transverse myelitis or optic neuritis or demyelination and India".