The aim of this study was to assess changes in the costs of asthma drug therapy before and during the use of chronic montelukast treatment in the U.K. A retrospective cohort analysis of a primary care database in the U.K. was carried out. Patients with chronic montelukast use (> or = 140 once-daily doses) were selected for analysis. Benchmarking data were obtained for matched patients with chronic inhaled corticosteroid (ICS) use and patients with chronic salmeterol therapy with concomitant ICS use. The main outcome measures were changes in utilization and monthly cost of asthma therapies costs. Asthma patients experienced significant (P<0.05) reductions in the monthly costs of ICS, short-acting beta-agonists and antibiotics following chronic montelukast therapy. Monthly concomitant drug costs were reduced by Pound Sterling 7.49 per month, which offset 27.5% of the additional cost of montelukast, yielding an increase in total drug costs of Pound Sterling 19.78 per month. Meanwhile, increased total drug costs for matched patients with chronic ICS use, and matched patients with chronic salmeterol therapy and concomitant ICS use, increased by Pound Sterling 5.37 per month and Pound Sterling 44.55 per month respectively. Additionally, patients using chronic montelukast therapy experienced a statistically significant (P<0.05) reduction in the use of short acting beta-agonists, and antibiotics, suggesting improvement in asthma control. Chronic use of montelukast therapy is associated with a reduction of concomitant drug therapy costs.