Introduction: Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory, demyelinating syndrome of the central nervous system (CNS) that predominantly affects the spinal cord and optic nerves. Since it was first described, new information about the pathophysiology gained momentum with the discovery of an antibody against aquaporin-4, a water channel protein that is predominantly found in the astrocytes. In our study, we evaluated the clinical features of NMOSD and clinically related CNS disorders.Method: In our study, we recruited patients that were followed by the Clinic for Multiple Sclerosis and Myelin Disorders at Istanbul University between 1979 and 2016.Results:Thirty-fiveNMOSD,fifteenrelapsinginflammatoryopticneuropathy (RION) and ten opticospinal multiple sclerosis (OSMS) patients were recruited in our study. Forty-eight patients (%80) were female,andtwelve(%20)weremale.Age,sex,follow-upperiod,annualized relapse rate, relapses in the first two years and progression index were similar between the groups. Cerebrospinal fluid (CSF) protein levels were higher in the NMOSD group. Concomitant autoimmune disorders were observed in six NMOSD patients and two OSMS patients. One patient with RION had nonspecific white matter lesions without gadolinium enhancement in the brain MRI.Conclusion: Laboratory and imaging findings suggests that NMOSD is a distinct disorder than RION and OSMS. Further studies are needed to make specific comments about the existence of OSMS.