This is a multi-center, randomized, double-blinded study in which approximately 210 RIS (radiologically isolated syndrome) subjects will be treated with either Tecfidera or placebo for 2 years (1:1 randomization). Study participants, along with the treating and examining physicians, will be blinded to treatment assignment. Central Clinical and Imaging Units will screen all potential study subjects for inclusion/exclusion criteria. We expect to enroll all RIS subjects within the U.S.