The PREVIA study was designed to investigate the role of montelukast, a leukotriene receptor antagonist, in the prevention of viral-induced asthma exacerbations in children aged 2 to 5 years with a history of intermittent asthma symptoms. The study was a 12-month multicenter, double-blind, parallel-group study of patients with asthma exacerbations associated with respiratory infections and minimal symptoms between episodes. Patients were randomized to receive oral montelukast 4 or 5 mg (depending on age) (n = 278) or placebo (n = 271) once per day for 12 months. Caregivers recorded children's symptoms, beta-agonist use, and health care resource use in a diary card. Over 12 months of therapy, montelukast significantly reduced the rate of asthma exacerbations by 31.9% compared with placebo. The average rate of exacerbation episodes per patient was 1.60 episodes per year on montelukast compared with 2.34 episodes on placebo. Montelukast also delayed the median time to first exacerbation by approximately 2 months (p = 0.024), and the rate of inhaled corticosteroid courses (p = 0.027) compared with placebo. Montelukast effectively reduced asthma exacerbations in 2- to 5-year-old patients with intermittent asthma over 12 months of treatment and was generally well tolerated.