Background. The efficacy of oral montelukast in chronic asthma is well established. Montelukast is also an effective adjunctive therapy to inhaled corticosteroids (ICS) in asthma uncontrolled on ICS alone. Inhaled montelukast was recently shown to provide significant bronchodilation compared with placebo in patients with chronic asthma. The purpose of this study was to evaluate the efficacy of inhaled montelukast added to inhaled mometasone. Methods. This was an 8-week, multicenter, randomized, double-blind, placebo-controlled study comparing once-daily inhaled montelukast 1 A mg plus inhaled mometasone 220 A μg (delivered by separate dry powder inhalers) with placebo plus inhaled mometasone 220 A μg. Men and women aged 15-85 years with chronic asthma, forced expiratory volume in 1 second (FEV1) 50-80% of the predicted value, and β-agonist reversibility ≥12% were eligible. Patients were required to meet a minimum symptom threshold while receiving open-label inhaled mometasone during a 3-week prestudy/run-in period. Patients received blinded (montelukast vs. placebo) treatment for 2 weeks, entered a 1-week washout period, then crossed over to the other treatment for 2 weeks. The primary endpoint was the average change from baseline in FEV1 over the 2-week treatment period. Secondary endpoints included daytime and nighttime symptom scores. Other endpoints included short-acting β-agonist (SABA) use, asthma exacerbations, asthma control, peak expiratory flow (PEF), and blood eosinophil count. Results. A total of 134 patients were randomized. For the primary endpoint, change from baseline in FEV1, inhaled montelukast plus inhaled mometasone was significantly more effective than placebo plus inhaled mometasone (least squares mean 0.22 AL vs. 0.17 A L; p A = A .033 [two-sided at α A = A 0.05]). Inhaled montelukast plus inhaled mometasone was also significantly more effective than placebo plus inhaled mometasone in improving daytime asthma symptom scores (p A = A .005) and nighttime asthma symptom scores (p A = A .015), increasing the percentage of days with asthma control (p A = A .004), decreasing the percentage of days with asthma exacerbations (p A ≤ A .001), and decreasing the blood eosinophil count (p A = A .013). Differences were not significant on AM or PM PEF or SABA use, although the latter approached significance (p A = A .073). Both treatments were well tolerated. Conclusion. Inhaled montelukast plus inhaled mometasone was significantly more effective than placebo plus inhaled mometasone in improving FEV1, symptoms, asthma control, and blood eosinophil count. © 2011 Informa Healthcare USA, Inc.