BACKGROUND. Recent studies have shown that the use of parenteral corticosteroids in the emergency department decreases the hospitalization rate for patients with acute asthma. We studied the efficacy of oral corticosteroids in the emergency department treatment of moderately ill children with acute asthma. METHODS. Emergency department patients aged 1 through 17 years whose chief complaint was acute asthma were assigned a pulmonary index, based on clinical evaluation. Those with a moderate exacerbation (pulmonary index = 9 through 13) received either 2 mg/kg of oral prednisone or placebo in a randomized, double-blind fashion. Patients in each group were then treated with an identical regimen of frequent aerosolized albuterol, for up to a maximum of 4 hours. RESULTS. Seventy-five patients were assessed. Overall, 11 (31%) of 36 in the prednisone group required hospitalization compared with 19 (49%) of 39 in the placebo group (P = .10). Among the sickest patients (initial pulmonary index > 10), 7 (32%) of 22 prednisone-treated patients required hospitalization compared with 13 (72%) of 18 placebo-treated patients (P < .05). Among patients who had a suboptimal response to initial beta 2-agonist therapy and who therefore would have been hospitalized had treatment been restricted to 2 hours, 9 (45%) of 20 in the prednisone group ultimately required hospitalization when duration of care was extended 2 additional hours compared with 15 (83%) of 18 in the placebo group (P < .05). In addition, prednisone-treated patients had a significantly greater improvement in median pulmonary index (5.0 vs 3.0, P < .001). CONCLUSIONS. These data demonstrate that oral prednisone, within 4 hours of its administration, reduced the need for hospitalization among a subset of children treated in the emergency department for acute asthma.