Approximately 50% of people diagnosed with Multiple Sclerosis (MS) will develop problems with cognition. Currently, there are no FDA-approved treatments for cognitive function in Multiple Sclerosis. Multiple sclerosis relapses are known to be significantly decreased by approximately 80% during late pregnancy. This disease improvement may be due to estriol, an estrogen unique to pregnancy. Estriol blood levels go from undetectable levels prior to pregnancy, increase during pregnancy and reach highest levels during late pregnancy. Further, estrogen treatment has been shown to have favorable effects on cognition in animal models of other neurological diseases. This proposal will establish whether oral treatment with estriol, induces an improvement in cognitive functioning in subjects with multiple sclerosis when used in combination with the major FDA-approved standard treatments for MS, (Betaseron® (or Extavia®), Rebif®, Avonex®, Copaxone®, Gilenya®, Aubagio®, or Tecfidera®).