Background Inhaled glucocorticosteroids (GCS) are the most effective long-term controller medications for the treatment of persistent asthma. Currently, however, available delivery devices limit their use in young children. A nebulized formulation of budesonide has been developed to address the needs of infants and young children. Objective To evaluate the efficacy and safety of once-daily budesonide inhalation suspension in children 6 months to 8 years old with mild persistent asthma not on inhaled GCS. Methods Three hundred fifty-nine children were randomized to receive once-daily budesonide inhalation suspension (0.25 mg, 0.50 mg, or 1.0 mg) or placebo via a Pari LC-Jet Plus™ nebulizer for 12 weeks. Efficacy assessments included nighttime/daytime asthma symptoms, pulmonary function (subset of patients), rescue medication use, and treatment discontinuations. Safety was based on adverse events and assessment of HPA-axis function. Results Demographics, baseline characteristics, asthma symptoms, and pulmonary function were similar across treatment groups. Mean nighttime/daytime asthma symptom scores were 1.19 ± 0.63 and 1.34 ± 0.53, respectively. Mean duration of asthma was 36.3 months and mean FEV 1 was 81.3% of predicted with 27.7% reversibility. Following 12 weeks of treatment, all budesonide inhalation suspension doses produced significant improvements in nighttime/daytime symptoms ( P ≥ .049) and significant decreases in rescue medication use ( P ≥ .038) compared with placebo. Significant improvements ( P ≥ .044) in FEV 1 were observed in the 0.5- and 1.0-mg budesonide inhalation suspension groups. There were no differences between doses of budesonide inhalation suspension. Adverse events and basal and ACTH-stimulated cortisol levels were similar among all groups. Conclusion Once-daily administration of budesonide inhalation suspension was well tolerated and effective for the treatment of mild persistent asthma in infants and young children not adequately controlled with bronchodilators or non-GCS antiinflammatory treatments.