The aim of this prospective, randomised, double blind study was to evaluate whether inhaled nebulized corticosteroid is effective in the treatment of croup. Thirty-seven children (aged 0.4-4.9 years) admitted to hospital with moderate to severe croup were allocated to treatment with either 2 mg nebulized budesonide (20) or saline (17). Disease severity was assessed by a clinical croup score based on stridor, cough, retractions, dyspnoea and cyanosis, and the overall clinical assessment was scored on a visual log scale (0-100). Two hours after treatment there was a significant improvement in croup score in the group treated with budesonide (8 to 4.5), but not in the group treated with saline (8 to 8). Furthermore, the overall clinical assessment score decreased significantly (50 to 25) in the group treated with budesonide, whereas it remained constant in the placebo group (60 to 62). The results indicate that nebulised budesonide can be used as a safe and effective alternative treatment in children with moderate to severe croup.