Objective: To determine the effect of repeated prone positioning (supine-prone/prone-supine) on oxygenation in children suffering from ARDS. Design: Single-center prospective case series. Setting: University pediatric ICU. Patients: Consecutive pediatric patients with severe ARDS (PaO2/FiO(2) <200, Murray score >2.5). Interventions: Patients were treated as soon as possible with supine-prone/prone-supine positioning every 8 h until clinical improvement or death occurred. Measurements and results: Twenty-three patients who had ARDS (0.5-months to 12.6-years-old), were placed in the prone position within 56 +/- 109 h after the diagnosis of ARDS. Prone-supine/supine-prone postural changes were repeated every 8 h for 9.7 +/- 5.5 days. Changes in PaO2/FiO(2) ratio during supine-prone and prone-supine positioning were evaluated. A positive change was defined as an increase of 15% of baseline value. The patient was classified as a responder when the mean increase in the prone position was greater than 15%. There were 18 responders and five non-responders. The responders showed an increase in PaO2/FiO(2) ratio of 22%, from 91 +/- 33 to 112 +/- 43 (P <0.001), when they were placed from the supine to the prone position. Their PaO2/FiO(2) ratio 0dropped from 109 +/- 37 to 94 +/- 36, P = 0.011, when changed from the prone to supine position. The overall mortality rate in this series was 48% (11 patients), which was higher in the non-responders (80%) than in the responders (39%), although this difference was not statistically significant (P = 0.95). Conclusions: The prone position improves oxygenation in a significant proportion of children with ARDS. Although no statistically significant difference was found for the mortality rate, it was higher for the non-responders (80%) vs the responders (39%).