OBJECTIVES: To estimate the budgetary impact of RRMS treatment from the perspective of the NHS in Spain (valued Euros-2011), in order to determine which treatment is most efficient from the payer’s perspective. METHODS: IMS sales data for multiple sclerosis drugs were used to estimate the total number of patients treated with each of the drugs used during 2011. The number of patients receiving treatment was calculated from the yearly cost of each treatment per patient (ex-factory price excluding VAT) because IMS presents total sales expressed as ex-factory price, which means that the yearly cost of the drug expressed as ex-factory price must be used to estimate the number of patients from the IMS sales data. Although there are clear differences in the effectiveness of the treatments used, these differences do not always explain differences in prices (higher incremental costs). RESULTS: Total expenditure in Spain in 2011 was €259 million. Among the patients, 47% were treated with interferon beta-1a, 27% with interferon beta-1b, 16% with glatiramer acetate and 10% with natalizumab. In the unlikely event that all patients had used interferon beta-1a in Spain, total expenditure would have been between -10% and +6.3%, depending on the drug used. If interferon beta 1b had been used by all patients, the total savings in Spain during 2011 would have been over 12.5%. Nonetheless, the greatest savings (>15% of total expenditure) would have been achieved if all patients had been treated with glatiramer acetate. CONCLUSIONS: Despite the limitations of the study (only direct drug costs were considered and the number of patients receiving treatment was extrapolated) this methodology may aid decision-making by policy makers, especially in times of economic difficulty, by showing which medication is more efficient.