OBJECTIVES: Medication adherence in chronic diseases like multiple sclerosis plays an important role in predicting long term outcomes. Data on medication adherence with disease modifying treatments (DMTs) are available for the treatment of multiple sclerosis (MS), However, such adherence comparisons between employees on different DMTs are not available. The Study Objective was to compare adherence among employees treated with DMTs for MS. METHODS: A healthcare claims database of US employees from 2001-2008 was used to identify patients with MS. Patients with two or more DMT prescriptions or 1 DMT prescription with a MS diagnosis [ICD-9=340.X]). Employees continuously employed and with health plan coverage for one year following DMT initialization were eligible. Two measures were used in estimating adherence after DMT initialization: a) annual persistence, defined as the sum of days with a medication supply prior to any 30-day gap in supply and b) medication possession ratio (MPR), defined as the number of days with a medication supply divided by 365 days. Wilcoxon tests on Kaplan Meier survival data and t-tests were used to compare persistence and MPR, respectively, between DMT groups. RESULTS: Overall, 358 employees [179=Avonex (Interferon [IFN]-β1a-IM); 63=Betaseron (IFN-β1b); 96=Copaxone (glatiramer acetate); 20=Rebif (IFN-β1a-SC)] were eligible for analysis. No significant differences in age, gender, and certain job-related variables existed between cohorts. Persistence was significantly better for Avonex than Betaseron (P=0.0096) and Copaxone (P=0.0004) and non-significantly better than Rebif (P=0.1207). Also, a greater proportion of Avonex employees were persistent at 1-year (60.89%) than Betaseron (42.86%, P=0.0131), Copaxone (42.71%, P=0.0039), and Rebif (45.00%, P=0.1700). Avonex also had the highest MPR (0.782) and was significantly higher than Copaxone (MPR=0.698, P=0.0160) and non-significantly higher than Betaseron (MPR=0.705, P=0.0576) and Rebif (MPR=0.761, P=0.7347). CONCLUSIONS: Among employees treated with Avonex, Betaseron, Copaxone and Rebif for MS, Avonex patients had significantly greater medication adherence.