BACKGROUND: The inhaled corticosteroid fluticasone furoate (FF) in combination with the long-acting β2-agonist vilanterol (VI) is under development for the treatment of asthma and chronic obstructive pulmonary disease. OBJECTIVE: To compare the efficacy and safety of FF-VI and FF in patients (≥ 12 years old) with persistent asthma. METHODS: In a randomized, double-blind, parallel-group study, patients (n = 609) (intent-to-treat population) received FF-VI 100-25 mcg, FF 100 mcg, or placebo once daily (evening) by using a dry powder inhaler for 12 weeks. Coprimary end points were change from baseline in trough FEV1 and serial (0-24 hours) weighted mean FEV1 (wmFEV(1)). Rescue-free 24-hour periods and safety also were assessed. RESULTS: Placebo increased trough FEV1 (196 mL) and wmFEV(1) (212 mL) versus baseline. Compared with placebo, FF-VI and FF significantly improved trough FEV1 (172 mL [P <.001] and 136 mL [P = .002]), respectively, and serial wmFEV(1) (302 mL [P <.001] and 186 mL [P = .003]), respectively. Treatment differences between FF-VI and FF approached significance for serial wmFEV(1) (116 mL; P = .060) but not for trough FEV1 (36 mL; P = .405). The percentage of rescue-free 24-hour periods with FF-VI was 10.6% greater than FF and 19.3% greater than placebo. Statistically significant (P = .032) urinary cortisol suppression was observed with FF-VI (ratio, 0.82) relative to placebo, but not with FF. Adverse event and safety profiles were similar across treatment groups. CONCLUSIONS: Significant improvement in lung function was observed with FF-VI and FF versus placebo in patients with persistent asthma. Improvement of FEV1 when VI was added to FF was not significant. The high placebo response in evening trough FEV1 may have influenced the assessment of efficacy.