OBJECTIVES: The objective of this study was to compare costs and effects of montelukast (MON) as add-on to inhaled corticosteroids (ICS) with long-acting â2 agonist (LABA) as add-on to ICS in adult patients with asthma when compliance is taken into consideration and from a Swedish health care sector perspective. METHODS: A health economic model was developed to calculate the incremental cost utility ratio of MON compared to the LABA salmeterol (SAL). Head-to-head data from IMPACT, a 2-year 48-week clinical study (N=1490) of patients with moderate asthma, was used in the model to estimate the relative effectiveness of the two regimens. The relative compliance for SAL was assumed to be 0.8 vs 1.0 for MON in the base case scenario. The analysis included costs for drugs, asthma events and adverse events. Event rates and asthma specific quality of life data for MON and SAL treated patients were collected from the IMPACT trial, while resource utilization and unit costs to treat the events were collected from local sources. RESULTS: In comparison with SAL, MON is associated with somewhat higher cost, but has, due to similar efficacy and better compliance, better effectiveness (more prevented attacks and more QALYs gain), less asthma-related hospitalization, and less serious drug-related side effects. The incremental cost per QALY for MON+ICS compared to SAL+ICS after adjusting for relative compliance was 7 000 EUR per QALY in the base case. CONCLUSION: When added to ICS, MON compared to SAL shows a favorable cost-utility in Sweden. This conclusion was stable for reasonable variations in the modelling assumptions.