OBJECTIVES: The aim of this study is to evaluate the economic impact and the clinical consequences associated to the use of tiotropium, as an add-on to usual care, in patients with severe persistent asthma. METHODS: A previously published 1-week cycle Markov model was used to estimate the cost per QALY. The model includes a death state and six states defined according to asthma control and severity of eventual relapses: controlled, partly controlled, uncontrolled, non-severe exacerbation, severe exacerbation without hospitalisation and severe exacerbation with hospitalisation. Progression is simulated for lifetime, assuming a 5% discount rate. Clinical data and utility weights for states without exacerbations come from two similar phase 3 randomised and double blind clinical trials, in which 912 patients were followed for 48 weeks. For exacerbation states, utility weights come from published literature. Costs were assessed for both the payers’ and NHS perspectives, being resource consumption estimated via an expert panel with five experienced pneumologists. RESULTS: Tiotropium enables patients to live more time with controlled asthma and to suffer less exacerbations, thus allowing an incremental gain of 0.18 QALY (12.02 vs 11.84). For the payers’ perspective, tiotropium costs 7,038€ but savings with follow-up and exacerbations conduct to an incremental cost of 459€. Therefore the cost per QALY is 2,576€. The NHS co-payment rate for tiotropium is 69% but, as it benefits from most of the savings with follow-up and exacerbations, incremental cost is negative (-1.820€), making tiotropium a dominant alternative. Deterministic and probabilistic sensitivity analysis show that results are robust. CONCLUSIONS: Tiotropium enhances the quality of life of patients with severe persistent asthma, as it allows a better control of the disease and a reduction of exacerbations. This cost-utility analysis shows that, in the Portuguese setting, its use is cost-effective under the payers’ perspective and dominant under the NHS perspective.