OBJECTIVES: A budget impact model (BIM) was developed to estimate the economic impact of introducing beclomethasone/formoterol extrafine for the treatment of moderate to severe persistent asthma in most important Autonomous Communities in Spain. METHODS: Analytic model was based on data from disease prevalence, population growth, drug consumption, retail prices and market shares forecasting for most representative Autonomous Communities in Spain: Andalusia, Catalonia, Madrid, Vasc Country and Valencia. It takes the perspective of the Spanish National Pharmaceutical budget and time horizon considered was 5 years (5% annual discount rate). Drugs considered in the study were fluticasone/salmeterol, budesonide/formoterol and beclomethasone/formoterol extrafine. The model estimates the annual cost to treat patients with moderate to severe persistent asthma before and after the introduction of beclomethasone/formoterol extrafine. Costs are referred to year 2008. RESULTS: According to demographic forecasts and asthma prevalence, target population with moderate to severe persistent asthma treated with fixed dose combinations would be around 104,634 patients in year 2007 in Andalusia, 54,362 in Catalonia, 36,727 in Madrid, 16,311 the Vasc Country and 35,132 in Valencia. On average, cost per patient was estimated at €982 before the introduction of beclomethasone/formoterol extrafine on the Spanish pharmaceutical market and at €964 after its introduction. CONCLUSIONS: This study estimates that the introduction of beclomethasone/formoterol extrafine for the treatment of moderate to severe persistent asthma on different Autonomous Communities is going to represent a net savings in the pharmaceutical budget during the next 5 years of around €11 million in Andalusia, €5.8 million in Catalonia, €4 million in Madrid, €1.7 in the Vasc Country and €3.9 in Valencia.