The objective of this study was to describe the characteristics of children who required mechanical ventilation (MV)or extracorporeal membrane oxygenation (ECMO) support for respiratory syncytial virus (RSV) bronchiolitis, and to identify risk factors associated with disease severity assessed by duration of MV, mortality and need for ECMO.Ventilated children under 1 year of age admitted for bronchiolitis were retrospectively studied over the 8-year period 1996-2003.The study population included 151 children.Of these, 38.4%were born prematurely and 8.6%had bronchopulmonary dysplasia (BPD).The mean age at initiation of MV was 61 days (±63 days).Infants were ventilated for a mean of 7.8 days (±7.5 days).Multivariate analysis revealed that prolonged duration of MV (> 6 days, median value) was significantly associated with low gestational age (P = 0.02 for the group < 32 weeks), requirement of neonatal oxygen supplementation (P = 0.03), BPD (P = 0.02) and positive tracheal aspiration culture (P = 0.004), in particular for Haemophilus influenzae (P = 0.03).Fourteen infants required ECMO with a mean period of MV before ECMO of 3.9 days (±4.5 days).Amongst these infants, the frequency of BPD was significantly higher as compared with the others (P = 0.001).Four infants died (survival rate 71.4%).The mean duration of ECMO for survivors was 12.1 days (±3.3 days).Conclusion: The data suggest that gestational age, requirement of neonatal oxygen supplementation, bronchopulmonary dysplasia and tracheal colonisation with Haemophilus influenzae are correlated with prolonged mechanical ventilation in children with bronchiolitis.Only bronchopulmonary dysplasia was associated with a need for extracorporeal membrane oxygenation that may provide lifesaving support in infants refractory to conventional management. The objective of this study was to describe the characteristics of children who required mechanical ventilation (MV) or extracorporeal membrane oxygenation (ECMO) support for respiratory syncytial virus (RSV) bronchiolitis, and to identify risk factors associated with disease severity granted by duration of MV , mortality and need for ECMO. Ventilated children under 1 year of age admitted for bronchiolitis were retrospectively studied from the 8-year period 1996-2003. The study population included 151 children. These 38.4% were born prematurely and 8.6% had bronchopnulmonary The mean age at initiation of MV was 61 days (± 63 days). Infants were ventilated for a mean of 7.8 days (± 7.5 days). Multivariate analysis revealed that prolonged duration of MV (> 6 days, median value of neonatal oxygen supplementation (P = 0.03), BPD (P = 0.02) and positive tracheal aspiration cult (P = 0.02 for the group <32 weeks) (P = 0.004), in particular for Haemophilus influenzae (P = 0.03) .Fourteen infants required ECMO with a mean period of MV before ECMO of 3.9 days (± 4.5 days) .Amongst these infants, the frequency of BPD was clearly higher The mean duration of ECMO for survivors was 12.1 days (± 3.3 days). Conlusion: The data suggest that gestational age, requirement of neonatal oxygen (P = 0.001) .Four infants died (survival rate 71.4%). supplementation, bronchopulmonary dysplasia and tracheal colonisation with Haemophilus influenzae are associated with prolonged mechanical ventilation in children with bronchiolitis. Bronchopulmonary dysplasia was associated with a need for extracorporeal membrane oxygenation that may provide lifesaving support in infants refractory to conventional management.