Multiple sclerosis (MS) witnessed relevant therapeutic progress in the last decade. Following the extraordinary progress in the treatment of relapsing-remitting (RR) multiple sclerosis (MS), two major unmet needs remain to be addressed by translational research in this field: progressive MS and the dream of a world free of MS. As far as the latter is concerned, the investigators can hope to make the dream come true by understanding the etiology of the disease and hence design definitive cures. A more realistic and pragmatic perspective may be the prevention of the clinical onset of the disease, a research field that promises to become increasingly important as the integration of genetic data with endophenotypes, magnetic resonance imaging and other biomarkers ameliorates the ability to predict the development of the disease under clinical circumstance. Bacille Calmette-Guerin (BCG) vaccine has been tested with encouraging results in early MS and clinically isolated syndrome (CIS). The knowledge that disease-modifying therapies work best when used early in the demyelinating process raises the question about whether to try this approach - which is safe, cheap and handy - in individuals with radiologically isolated syndrome (RIS). Radiologically isolated syndrome is a new entity, diagnosed when the unanticipated magnetic resonance imaging (MRI) finding of brain spatial dissemination of focal white matter (WM) lesions highly suggestive of MS occurs in subjects without symptoms of MS, and with normal neurological examinations. Conversion to clinically isolated syndromes (CIS) were described in 84% of RIS individuals with spinal cord lesions over a median time of 1.6 years from the date of the first MRI. Whether or not to treat this condition remains currently a clinical conundrum. Bacille Calmette-Guérin (BCG) vaccine may have these characteristics since it resulted beneficial in early MS and first demyelinating episodes. Being safe, cheap and handy, the investigators propose to investigate its use to prevent progression of the demyelinating process in radiologically isolated syndrome. An approach such as BCG vaccine seems appropriate as a front-line immunomodulatory approach for RIS people. In a pilot study BCG vaccine was safe and effective in reducing disease activity at MRI, and the risk of developing persistent T1-hypointense lesions ('black holes' -BH- expression of tissue damage) in subjects with MS.