To assess factors associated with outcome in children admitted to paediatric intensive care (PIC) with bronchiolitis. A retrospective study of children admitted to the PICU at St Mary\'s Hospital, London with bronchiolitis over a 6-year period (2011-2016). All bronchiolitis admissions < 2 years were included. Data collected particularly noted risk factors for severity, demographics, microbiology and outcome. We compared respiratory syncytial virus (RSV) with non-RSV status. Multivariate analysis was performed. Two hundred seventy-four patients were identified. Median age was 60 days (IQR 28-150 days), 63% were male, 90% were invasively ventilated and 42% were previously healthy. Pre-existing co-morbidities were present in 38%. The most frequently isolated pathogens were RSV (60%) and rhinovirus (26%). Co-infection was present in 45%, most commonly with RSV, rhinovirus and bacterial pathogens. Median length of stay (LOS) was 6 days (IQR 4.75-10). Younger age, prematurity, RSV, co-infection and co-morbidity were identified as significant risk factors for prolonged LOS. Six children died. Five of these had documented co-morbidities. CONCLUSION: RSV causes more severe bronchiolitis than other viruses. Nearly half of children admitted to PICU with RSV were previously healthy. Current guidelines for immunoprophylaxis of RSV bronchiolitis should be re-considered. What is Known: * Bronchiolitis is one of the most common reasons for unplanned PICU admission. The most common virus causing bronchiolitis is RSV * Bronchiolitis severe enough to require admission to PICU is associated with frequent morbidity but has low mortality. What is New: * RSV causes more severe bronchiolitis than other viruses. * Nearly half of all children admitted to PICU with RSV were previously healthy.