OBJECTIVES: To compare outcomes of multiple sclerosis (MS) patients treated with either glatiramer acetate (GA) or low dose interferon beta 1-a (IFN-β-1a [IM]).METHODS:Data were obtained from i3’s Lab Rx Database from July 2001 to June 2006.  We established an “intent-to-treat” (ITT) cohort (N=1282) of patients diagnosed with MS who began therapy on either GA or IFN-β-1a [IM] and had continuous insurance coverage from 6 months before to 24 months after the identified first use of the medication.  We also created a “continuous use” (CU) cohort (n =639) of individuals who, in addition to the criteria listed above, used either GA or IFN-β-1a [IM] within 28 days of the end of the two year post-period. Using multivariate regressions, we examined both the two-year total direct medical costs and the likelihood of relapse associated with the use of each MS medication. Relapse is defined as either being hospitalized with a diagnosis of MS or being diagnosed with MS during an outpatient visit and then prescribed steroids within a 7-day period. All regression analyses evaluated a wide range of factors that may affect outcomes.RESULTS: In the ITT cohort,  compared to those who initiated therapy on IFN-β-1a [IM], patients who started therapy on GA had a significantly lower two-year risk of relapse (10.01% v 5.18%; p=0.0034) and significantly lower two-year total medical costs ($44,201 v $41,121; p=0.0294).  In the CU cohort, compared to those who used IFN-β-1a [IM], patients who used GA also had a significantly lower two-year risk of relapse (7.25% v 2.16%; P=0.0048)  and significantly lower total medical costs ($67,744 v $63,714; P=0.0445). CONCLUSIONS: Results from this study indicate that, compared to the use of IFN beta-1a [IM], GA use is associated with significantly lower probability of relapse and significantly lower two-year total direct medical costs.