Sex differences in the clinical course of multiple sclerosis were investigated in 947 patients with multiple sclerosis collected from all over Japan through the nationwide survey undertaken by the Multiple Sclerosis Research Committee of Japan from 1972 through 1973. A course of remissions and exacerbations, more frequent involvement of optic nerves, and more severe motor and visual disability were present in a higher proportion of women than men. These features corresponded to those which have been considered to characterize Oriental multiple sclerosis patients.