OBJECTIVES: The objective of this study is to conduct a health economic evaluation and compare the health care costs associated with patients diagnosed with relapsing remitting multiple sclerosis and taking Interferon beta 1b (Extavia) or Interferon beta 1a (Rebif) subcutaneously.   METHODS: A large US administrative retrospective claims database was used to identify patients diagnosed with RRMS and were prescribed Interferon beta 1b (IB1a) or 1a (IB1b) between January 2010 and December 2012 were included in the study. All patients were ≥ 18 years of age and continuously enrolled in the same health plan for a year. Descriptive statistics, chi-square tests and regression analysis were performed on the data and statistical significance level was set a priori at 0.05. RESULTS: There were a total of 317 patients on IB1a and 10,190 on IB1b that met study criteria. Patients on average were charged $3378.06±963.58 and $3985.06±1923.06 for their treatment (p<0.001) with IB1a and IB1b. However, the amount allowed (p<0.001) by the health plan was $3060.36±917.77 and $3633.22±1769.11 and the actual amount paid (p<0.001) was $2977.23±912.96 and $3521.31±1762.29 for a month supply. The annual cost of treating patients with IB1b was higher than IB1a ($40,536.80±11563.02 vs 47,820.77±23076.74, p<0.001). The majority of the IB1a and IB1b patients were charged anywhere between $50K and $100K (93.1% vs 80.0%) and a smaller percentage (0.9% vs 6.5%, p<0.001) of patients were charged over >$100K for their treatment per year. Patients on group coverage ($36,172.54±6049.21 vs $41,592.60±8714.17) had lower annual costs compared to patients on non-group coverage ($43,736.44±14846.43 vs $44,945.83±19077.93). The regression analysis shows that patients receiving drug supply >30 days, were on non-group coverage and patients receiving IB1b were more likely (p<0.05) to have higher annual charges.  CONCLUSIONS: Patients on IB1b treatment and non-group coverage had higher annual costs.