Inhaled steroids are recommended for long-term control of asthma, but their use may be limited in young children because of difficulties in using the associated inhaler device. The use of nebulizers may help to overcome this issue, without compromising therapeutic efficacy or safety. This 14-week, multicentre, randomized, controlled, open-label, parallel-group study compared the efficacy and safety of nebulized corticosteroids in paediatric patients (aged 6 months to 6 years) with severe persistent asthma. Beclometasone dipropionate (BDP) 800 microgday(-1) suspension for nebulization and budesonide (BUD) 750 microg day(-1) given by nebulization in a twice-daily regimen, and when used in addition to the usual maintenance therapy, resulted in comparable clinical efficacy across all parameters. The primary efficacy endpoint was the number of patients who did not experience any major exacerbation, this being 40.4% and 51.7% in the BDP and BUD groups respectively in the ITT population (P = 0.28), and the mean number of global exacerbations (major plus minor) decreased respectively by -37.5% in the BDP group and -23.3% in the BUD group. Both treatments were also associated with marked reductions in the number of nights with wheezing and the number of days of oral steroid use. Moreover, the two treatment groups had a similar adverse-event incidence and profile. Only 11 adverse events were reported, and no serious adverse events were related to treatment. Urinary cortisol and the time course of height and weight were unaffected by both treatments, and BDP was confirmed to have a neutral effect on bone metabolism. In conclusion, this study demonstrates that both BDP 800 microg day(-1) suspension for nebulization and BUD 750 microgday(-1) administered by nebulization are effective, with an acceptable safety profile, for treatment of severe persistent asthma in infants and young children.