Asthma is a heterogeneous condition characterized by reduced lung function, chronic inflammation, and periodic asthma deteriorations. This study was performed to evaluate the effect of mometasone furoate (MF)/formoterol (F) combination, 200/10 microg, administered twice daily (b.i.d.) on asthma deteriorations and pulmonary function in patients with asthma uncontrolled on medium-dose inhaled corticosteroid (ICS). After 2- to 3-week open-label run-in with MF 200 microg b.i.d., patients (>or=12 years) were randomized to 26 weeks of treatment with MF/F 200/10 microg, MF 200 microg, F 10 microg, or placebo b.i.d. Coprimary end points were time to first asthma deterioration (MF/F versus F) and bronchodilation, assessed by the area under the curve of the change in forced expiratory volume in 1 second 0-12 hours (FEV(1) AUC(0-12h); MF/F versus MF). A total of 781 patients were randomized. Treatment with MF/F 200/10 microg reduced asthma deteriorations and clinically judged deteriorations (i.e., deterioration resulting in emergency treatment, hospitalization, or treatment with additional excluded asthma medication [i.e., systemic corticosteroids]). The proportion of patients experiencing asthma deteriorations was MF/F, 30.4%; MF, 33.9%; F, 54.0%; placebo, 55.6% (p <0.001, MF/F versus F and placebo). There was a sixfold reduction in clinically judged deteriorations with MF/F versus F and placebo (p <0.001). Lung function improved more rapidly with MF/F than MF and placebo. Mean change from baseline FEV(1) AUC(0-12h) at week 12 was MF/F, 11.7% versus MF, 5.7%; F, 8.5%; and placebo, 3.9% (p <0.001). Treatment-related AEs were rare and similar across groups. Treatment with MF/F 200/10 microg was effective in reducing the risk of asthma deteriorations. MF/F was safe and provided rapid and sustained bronchodilation in patients with asthma.