We reviewed the clinical and immunological features of optic-spinal multiple sclerosis (OSMS), or relapsing neuromyelitis optica. OSMS has collected much attention as to whether it is a distinct entity from conventional MS (CMS). However, OSMS plus minor cerebral and brainstem/cerebellar involvement and the later conversion into CMS had been a diagnostic dilemma. To overcome such problems and delineate the features of OSMS, we analyzed 'Pure OSMS' with which patients had only relapsing optic neuritis and myelitis clinically and consistently normal brain MRI during 5 years or longer follow-ups. As a result, we found that this type of MS was characterized by a definite female preponderance and negative oligoclonal IgG bands (OB), although 'Pure OSMS' was heterogeneous with regards to the clinical severity and HLA class II alleles. Previously reported immunological data in OSMS include negative OB and no elevation of IL-10 or matrix metalloproteinase-9 in the cerebrospinal fluid (CSF) during relapses. In addition, we recently demonstrated that the CCR5+ Th1 cell subset in CSF during relapses, which significantly increased in CMS, remained low in OSMS. These unique clinical and immunological findings probably relate to fundamental differences in the pathogeneses of OSMS and CMS and deserve further characterization.