Objective: To analyse the cost-effectiveness (C-E) of interferon therapy for MS and the impact of adherence associated with a patient support programme (PSP). Methods: Markov model was structured based on systematic review of the evidence and the opinion of local experts. The model has three health states: (1) Baseline treatment (BT), (2) Interferon-β (IFN) with patient support programme (PSP) and (3) IFN without PSP. Annual cycles were considered, with a time horizon of 30 years. The analysis perspective was based on the Ministry of Health (MoH). Key findings: Interferon-β + PSP dominates the treatment of IFN without PSP. The incremental C-E rate (ICER) for IFN + PSP was estimated at S/. 26 408 per Quality Adjusted Life Year (QALY) in relation to BT. IFN without PSP was dominated by the IFN + PSP treatment. The cost per QALY of IFN + PSP was below the payment threshold in almost 100% of the model simulations. The acceptability curves show that the treatment with PSP + IFN is probabilistically more cost effective from a payment threshold of 1.25 annual Gross Domestic Product per capita (GDP-pc). The Tornado analysis for the ICER between IFN + PSP and BT shows that the most sensitive variables of the model are the relative risk (RR) for treatment adherence and the cost of IFN + PSP treatment. Conclusion: The addition of a PSP had a significant effect on adherence and C-E of the intervention. The ICER for IFN + PSP was below 1.5 annual GDP-pc of payment threshold with an incremental cost near to 3 GDP-pc. IFN without PSP was dominated by the IFN + PSP.