Objective: To evaluate the effect of systemic prednisolone as an adjunct to conventional treatment with beta2-agonist, respiratory support, and fluid replacement in hospitalized infants <24 months of age with respiratory syncytial virus (RSV) infection. Methods: The study was randomized, double-blind, and placebo-controlled. During the winter of 1995-1996, 147 infants <2 years of age, hospitalized with RSV infection, were allocated to treatment with either systemic prednisolone mixture 2 mg/kg daily or placebo for 5 days. MAIN OUTCOME MEASURES: The acute effect variables were duration of stay in hospital, use of medicine, and supportive measures while in hospital. At follow-up 1 month after discharge, the acute effect variables were duration of illness, start in day care center, morbidity, and use of medicine. At follow-up 1 year after discharge, the acute effect variables were morbidity, use of medicine, and skin prick tests with allergens. RESULTS: Prednisolone treatment had no effect on any of the outcome measures. CONCLUSIONS: Our randomized prospective study in infants hospitalized with acute RSV infection showed no effect of systemic prednisolone treatment either in the acute state of RSV infection, nor in the follow-up 1 month and 1 year after admission to hospital. We find our results in agreement with the largest studies reported earlier; therefore, corticosteroid, whether by the systemic route or by inhalation, should not be prescribed to infants with RSV infection.