OBJECTIVES: Daclizumab, a third line agent for treatment of MS was approved by the FDA in May 2016.The study aimed to evaluate the cost-effectiveness of daclizumab versus interferon beta-1a in the treatment of patients with relapsing-remitting multiple sclerosis (RRMS) in United States (US), from a third party payer perspective. METHODS: A static decision model was developed in Microsoft Excel® over a three year time horizon. Model inputs were drug acquisition costs (wholesale acquisition costs from 2018 RED BOOK Online®); drug administration and monitoring costs (package inserts, Healthcare Bluebook and Centers for Medicare & Medicaid Services 2018 Physician Fee Schedule); relapse rates and relapse rate reduction from DECIDE trial of daclizumab and interferon beta-1a as the active comparator. Cost of managing relapses was taken from published literature. All costs were adjusted for 2017 US dollars using the Consumer Price Index. Outcomes measured included total cost of therapy per patient, cost per relapse avoided and incremental cost effectiveness ratios (ICERs) calculated as incremental cost per relapse avoided. Univariate sensitivity analysis was conducted to test model robustness over a range or ± 20% (wherever ranges were not available). RESULTS: Total costs over a 3-year period was $267,474.84 for daclizumab and $273,709.39 for interferon beta-1a. Daclizumab had higher relapse avoided per patient (0.84) compared to interferon beta-1a (0.43). The cost per relapse avoided was $318,422.43 for daclizumab compared to $636,533.47 for interferon beta-1a. Daclizumab was more effective and less costly than interferon beta-1a and thus, dominated interferon beta-1a. The univariate sensitivity analysis indicated that results varied with potential changes in drug costs. CONCLUSIONS: The study suggested that daclizumab was dominant compared to interferon beta-1a in the treatment of RRMS from a US payer perspective. In patients with RRMS, daclizumab is thus an effective therapy choice in this model.