OBJECTIVES:  To evaluate the economic and clinical impacts of treatment with subcutaneous peginterferon beta-1a (SC PEG-IFN) vs. SC interferon beta-1a (SC IFN beta-1a) for relapsing-remitting multiple sclerosis (RRMS) in five European countries (EU5): France, Germany, Italy, Spain, and UK. METHODS:  A cost-consequence model, from the national payer perspective, was developed to compare country-specific costs of treating patients with SC PEG-IFN vs. SC IFN beta-1a. The model evaluates clinical and economic consequences of switching all patients who are currently on SC IFN beta-1a to SC PEG-IFN. A Markov model over two years with three month cycles was computed. Costs of relapse and disability status are from a cross-sectional cost of illness study (Kobelt et al. 2016). The annualized relapse rate and confirmed disability progression hazard ratios for SC PEG-IFN vs. SC IFN beta-1a were estimated using the results from Tolley et al. 2015 and Coyle et al. 2016. The RRMS populations treated with SC IFN beta-1a are from actual 2016 utilization. RESULTS:  The number of RRMS patients treated with SC IFN beta-1a ranged from 2,810 in France to 11,699 in Germany. The use of SC PEG-IFN in place of SC IFN beta-1a reduced the number of relapses, and cost of DMT, relapse, and disability status in each country. The sum of these cost savings ranged from €9,514,404 in France to €61,955,057 in Germany, for a total savings of €178,871,314 over two years (64.2% due to drug, 27.1% to relapse, and 8.7% to disability status cost savings) across the EU5. Total savings per patient ranged from €3,460 in France to €10,865 in Spain. CONCLUSIONS: These results suggest that use of SC PEG-IFN compared with SC IFN beta-1a in the treatment of RRMS is a cost-saving strategy in the EU5. Additional research incorporating adherence and side effects are necessary to analyze treatment options.