OBJECTIVES To examine claims-based relapse rates and time to relapse among multiple sclerosis (MS) patients treated with natalizumab or propensity score matched patients treated with platform therapy (interferon beta/glatiramer acetate) in the US.  METHODS The Truven Health MarketScan Research Databases were used to identify adults with a MS (ICD-9-CM code 340) diagnosis treated with natalizumab or platform therapy; the first claim between January 1, 2009 and April 1, 2012 was the index.  Patients had to have one year continuous enrollment pre- and post-index and remain on index therapy for 12 months. Patients were excluded if they used a non-index therapy in the pre-index.  Natalizumab and platform patients were propensity scored matched using nearest neighbor matching on demographic characteristics, selected comorbid conditions and medications, MS severity (using an adaptation of Kurtzke’s Functional System), pre-index relapse and pre-index expenditures.  MS-relapse was defined as MS-related inpatient (IP) admission, IV or oral corticosteroid use.  Cox Proportional Hazard models were used to evaluate time to relapse, controlling for demographic and pre-index clinical characteristics. RESULTS A total of 897 natalizumab patients met the study criteria, 882 of which were 1:1 matched to 882 platform therapy patients (mean age 45 years, 70% female) with a standardized difference <10 on all matching measures. Compared to platform patients, natalizumab patients were significantly less likely to have MS-relapse post-index (26.5% vs. 35.5%, p<0.001), with lower post-index rates of MS-related IP admissions (1.0% vs. 2.6%), IV-corticosteroid use (15.6% vs. 19.0%) and oral corticosteroid use (15.4% vs. 23.1%) (all p<0.001). Natalizumab patients also had 25 more relapse-free days (308 vs. 283 days, p<0.001). Post-index MS-relapse risk was lower for natalizumab patients (HR=0.69, p<0.001) after controlling for baseline characteristics.  CONCLUSIONS Natalizumab was associated with a significantly lower risk and rate of MS-relapse and had longer time to a MS-relapse compared to platform therapy.