This article reviews the short-term and long-term safety profile of budesonide inhalation suspension (BIS) for nebulization in infants and young children with persistent asthma. Short-term safety (12 weeks) was assessed by pooling the results from the 3 randomized, double-blind, placebo-controlled, multicenter studies (studies A, B, and C) on the efficacy and safety of once- and twice-daily BIS. Long-term safety of BIS and conventional asthma therapy (CAT) was assessed in 52-week extension studies of the 12-week double-blind trials. CAT consisted of any available therapy for asthma; in 2 studies, CAT could have included treatment with inhaled glucocorticosteroids. Safety was assessed by monitoring adverse events (AEs), physical examinations, and basal and ACTH-stimulated plasma cortisol levels (in a subset of subjects). In the 52-week open-label extensions, the effects of BIS on growth velocity and skeletal age also were determined. In the 12-week studies, a total of 1017 subjects was evaluated for safety; totals of 231, 185, 229, 327, and 45 subjects were randomized to receive placebo or BIS at total daily doses of 0.25 mg, 0.5 mg, 1.0 mg, and 2.0 mg, respectively. Subject demographics and baseline asthma characteristics were similar across treatment groups, except that age, weight, height, and duration of asthma appeared higher in the 2. 0-mg daily dose group. For BIS groups, mean age was 58.9 months; mean weight was 20.3 kg; mean height was 108.9 cm, and mean duration of asthma was 3.2 years. There were no differences in the incidence, severity, or types of AEs reported among the BIS and placebo groups. There were no significant differences between placebo and BIS treatment groups in basal or ACTH-stimulated cortisol levels, physical examinations, clinical laboratory values, or fungal cultures. A total of 670 subjects completed the 52-week extension studies; 223 subjects received CAT and 447 received BIS. Median total daily doses of BIS ranged from 0.50 mg to 1.0 mg in the 3 studies, and the mean duration of treatment exposure was 304 +/- 119 days and 342 +/- 83 days in CAT and BIS groups, respectively. During the 52-week treatment period, the incidences of reported AEs were comparable between treatment groups and were mild-to-moderate in intensity; no new AEs occurred during the 52-week studies compared with 12-week studies. No significant differences were observed between BIS and CAT in basal or ACTH-stimulated cortisol levels, physical examinations, clinical laboratory values, or fungal cultures. There was a small but statistically significant reduction in growth velocity (a difference of 0.8 cm) in the BIS-treated group compared with the CAT group in study A. In studies B and C, growth velocity was not different between BIS and CAT groups. In pooled analyses, no statistically significant differences in growth velocity, standard median heights, or skeletal age were observed between BIS and CAT groups. Short-term and long-term treatment with BIS, over a wide range of doses, was well tolerated for the treatment of persistent asthma in infants and young children.