Asthma control is improved by combining inhaled corticosteroids with long-acting beta2-agonists. However, fluctuating asthma control still occurs. We hypothesized that in patients receiving low maintenance dose budesonide/formoterol (bud/form), replacing short-acting beta2-agonist (SABA) reliever with as-needed bud/form would provide rapid symptom relief and simultaneous adjustment in antiinflammatory therapy, thereby reducing exacerbations. In this double-blind, randomized, parallel-group study, 2,760 patients with asthma aged 4-80 years (FEV1 60-100% predicted) received either terbutaline 0.4 mg as SABA with bud/form 80/4.5 microg twice a day (bud/form + SABA) or bud 320 microg twice a day (bud + SABA) or bud/form 80/4.5 microg twice a day with 80/4.5 microg as-needed (bud/form maintenance + relief). Children used a once-nocte maintenance dose. Bud/form maintenance + relief prolonged time to first severe exacerbation (p < 0.001; primary endpoint), resulting in a 45-47% lower exacerbation risk versus bud/form + SABA (hazard ratio, 0.55; 95% confidence interval, 0.44, 0.67) or bud + SABA (hazard ratio, 0.53; 95% confidence interval 0.43, 0.65). Bud/form maintenance + relief also prolonged the time to the first, second, and third exacerbation requiring medical intervention (p < 0.001), reduced severe exacerbation rate, and improved symptoms, awakenings, and lung function compared with both fixed dosing regimens.