We proved an overview of prevention medicine in neuroimmunological disease, especially focusing on multiple sclerosis (MS). Due to lack of large–scale primary–prevention studies, there are no concrete data on primary prevention for MS. Therefore, in this review article, we discussed risk factors for developing and worsening MS, including genetic factors (HLA), environmental factors (viral infection and sunlight exposure), and non–environmental factors (cigarette smoking). We also commented on secondary prevention therapies for MS currently available in Japan, including natalizumab, ofatumumab, fingolimod, siponimod, dimethyl–fumarate, glatiramer acetate, and interferon beta I a/b.