Résumé : Objective:To determine the efficacy of dexamethasone in the treatment of mechanically ventilated children with respiratory syncytial virus–severe lower respiratory tract infection.Design:International, multicenter, randomized, double-blind, placebo-controlled trial.Setting:Twelve pediatric intensive care units.Subjects:Children (<2 yrs) mechanically ventilated for respiratory syncytial virus lower respiratory tract infection. Children were prestratified for severity of oxygen abnormalities on admission.Intervention:Intravenous dexamethasone (0.6 mg/kg/day, 48 hrs) or placebo.Measurements and Main Results:A superiority approach was used in the subgroup of patients with mild oxygen abnormalities (arterial partial pressure of oxygen/fractional inspired oxygen concentration [PaO 2 /Fio 2 ] >200 mm Hg and/or mean arterial pressure ≤10 cm H 2 O) and a noninferiority approach in those with severe oxygen abnormalities (PaO 2 /Fio 2 ≤200 mm Hg and mean arterial pressure >10 cm H 2 O). Primary outcome was the duration of mechanical ventilation. In the subgroup with mild oxygenation abnormalities, 45 of the 89 included patients received dexamethasone and 44 placebo; in the subgroup with severe oxygenation abnormalities, 28 of the 56 included patients received dexamethasone and 28 placebo. Baseline characteristics in both treatment arms were similar for both subgroups. After the third interim analysis, the trial was stopped early for futility taking the slow enrollment into account. At that time, the median duration (interquartile range) of mechanical ventilation was 137 (91–195) hrs in the dexamethasone- and 139 (117–188) hrs in the placebo-treated patients in the subgroup with mild oxygenation abnormalities ( p = .6). In the subgroup with severe oxygenation abnormalities, it was 171 (136–212) hrs in the dexamethasone- and 170 (125–201) hrs in the placebo-treated patients ( p = .6).Conclusion:In this prematurely ended trial in children mechanically ventilated for severe respiratory syncytial virus–lower respiratory tract infection, we found no evidence of a beneficial effect of dexamethasone in children with mild oxygenation abnormalities. Neither was evidence found that dexamethasone may prolong mechanical ventilation in those with severe oxygenation abnormalities.