Many studies have attempted to find out whether steroid treatment is beneficial in children with croup, but the results have been inconclusive. We have done a prospective placebo-controlled study of the effect of prednisolone on two clinical endpoints-the duration of intubation and the need for reintubation.Reasons for exclusion were age under 6 months, congenital airway anomalies, and previous intubation. 70 eligible children were randomly assigned treatment with prednisolone 1 mg/kg (n = 38) or placebo (n = 32) every 12 h given by nasogastric tube until 24 h after extubation. 11 (34%) placebo-treated and only 2 (5%) prednisolone-treated patients required reintubation after accidental or elective extubation (p = 0.004, Fisher's exact test; odds ratio 8.9, 95% confidence interval 1.7-59.3). Survival analysis with log-normal regression showed that the duration of intubation was shorter with steroid therapy (p <0.003) and increasing age (p <0.02), but was not influenced by endotracheal tube size or abnormality on chest radiograph. The median duration of intubation was 138 (95% CI 118-160) h in children who received placebo and 98 (85-113) h in the prednisolone group.Steroid therapy reduces the duration of intubation and the need for reintubation in children intubated for croup.