Surgical treatment of disabling multiple sclerosis (MS) tremor that does not respond to medication has proven difficult. To date, there have been no prospective blinded studies to evaluate efficacy of surgical treatments for these tremors. Based on prior data, this study will examine the use of 2 DBS electrodes on the same side of the brain in the thalamus region (one at an area referred to as the "ventralis intermedius nucleus/ventralis oralis posterior nucleus border," or "VIM," and one at a region called the "ventralis oralis anterior nucleus/ventralis oralis posterior nucleus border," or "VO") for treatment of MS tremor. This study will test the effectiveness of VIM combined with, and independent of, VO DBS, and characterize safety, benefits and side effects of this procedure for treatment of MS-related tremors.