Devic's neuromyelitis optica (NMO) is a neurological condition characterized by a severe involvement of the optic nerves and spinal cord in a mono- or multi-phasic manner. Recent pathologic, cerebrospinal fluid and conventional magnetic resonance imaging (MRI) studies have shown abnormalities which might help in differentiating patients with NMO from those with multiple sclerosis. This review article summarizes the main results obtained using conventional MRI in NMO, which has contributed to the definition of internationally-accepted diagnostic criteria, and those obtained from the application of modem quantitative MR techniques which are significantly changing our views on NMO pathobiology.