The primary objective of this initiative is to assess the effectiveness of subcutaneous (sc) interferon (IFN) beta - 1a, (Rebif®), versus No Treatment in delaying the conversion to Clinically Definite Multiple Sclerosis (CDMS) - as defined by the occurrence of a second exacerbation - over 96 weeks in subjects that present with Clinically Isolated Syndrome (CIS) accompanied by an abnormal magnetic resonance imaging (MRI). The secondary objectives are to: