To compare the benefits of noninvasive ventilation (NIV) plus standard therapy vs. standard therapy alone in children with acute respiratory failure; assess method effectiveness in improving gas exchange and vital signs; and assess method safety. Prospective, randomized, controlled study. SITE: Two pediatric intensive care units in Santiago, Chile, at Clínica Santa María and Clínica Dávila, respectively. Fifty patients with acute respiratory failure admitted to pediatric intensive care units were recruited; 25 patients were randomly allocated to noninvasive inspiratory positive airway pressure and expiratory positive airway pressure plus standard therapy (study group); the remaining 25 were given standard therapy (control group). Both groups were comparable in demographic terms. The study group received NIV under inspiratory positive airway pressure ranging between 12 cm and 18 cm H2O and expiratory positive airway pressure between 6 cm and 12 cm H2O. Vital signs (cardiac and respiratory frequency), Po2, Pco2, pH, and Po2/Fio2 were recorded at the start and 1, 6, 12, 24, and 48 hrs into the study. Heart rate and respiratory rate improved significantly with NIV. Heart rate and respiratory rate were significantly lower after 1 hr of treatment compared with admission (p = 0.0009 and p = 0.004, respectively). The trend continued over time, heart rate being significantly lower than control after the first hour and heart rate after 6 hrs. With NIV, Po2/Fio2 improved significantly from the first hour. The endotracheal intubation was significantly lower (28%) in the NIV group than in the control group (60%; p = 0.045). NIV improves hypoxemia and the signs and symptoms of acute respiratory failure. NIV seems to afford these patients protection from endotracheal intubation.