OBJECTIVES: To determine cost-utility of pegylated interferon beta-1a (PegINFβ-1a) versus interferons beta-1a (INFβ-1a) and beta-1b (INFβ-1b) in patients with Relapsing-Remitting Multiple Sclerosis (RRMS) in Colombia. METHODS: The base case patient has a RRMS severity <2.5 according to Expanded Disability Status Scale, the perspective of analysis was from Colombian health system. Time horizon was 20 years; the annual discount rate was 5% for benefits and costs. Outcomes: proportion of patients without relapsing during 24 months, survival rate at 20 years, Quality-Adjusted Life Years (QALYs). Direct costs were calculated for the year 2016. A Markov decision model was constructed in a hypothetical cohort of 1000 patients, considering ten RRMS’ states. The model represents the probabilities of moving from state to state, leaving the treatment and dying. RESULTS: Clinical efficacies are: PegINFβ-1a, 39%; INFβ-1a, 23.9%; INFβ-1b, 13.7%. Most common complications include depression (53%), spasticity (49%) and fatigue (70%). Total discounted costs to 20 years are: no treatment, US$ 47,015; PegINFβ-1a, US$ 173,708; INFβ-1a, US$ 210,365; INFβ-1b, US$ 165,267. Discounted QALYs to 20 years in 1000 patients are: no treatment, 7,435; PegINFβ-1a, 9,293; INFβ-1a, 8,601; INFβ-1b, 8,104. ICER versus no treatment are: PegINFβ-1a, US$ 68,175; INFβ-1a, US$ 140,040; INFβ-1b, US$ 176,674. Survival rates to 20 years are: no treatment, 68.3%; PegINFβ-1a, 92.0%; INFβ-1a, 86.9%; INFβ-1b, 76.6%. To willingness to pay higher than US$ 80,000, PegINFβ-1a has a probability higher than 85% to be the chosen treatment, for lower values, the highest probability is no treatment strategy. In the univariate sensitivity analysis, PegINFβ-1a is dominant over INFβ-1a in all scenarios of costs, and PegINFβ-1a is dominant over INFβ-1b on scenario at the minimum cost of PegINFβ-1a. CONCLUSIONS: PegINFβ-1a is the most cost-effective strategy in patients with RMSS, both in terms of improved survival and long term QALYs as well as in terms of lowest ICER.