Objective: To investigate tidal volume (VT) and leak measurements during continuous positive airway pressure (CPAP) in neonates using a commercial ventilatory device equipped with a flow sensor at the Y-piece.Design: Randomized cross-over trial.Setting: Neonatal intensive care unit level III. Patients: Thirty-two infants, median (range) birth weight 1,435 (710-2,730) g, gestational age 30 (24-38) weeks.Interventions: During nasopharyngeal CPAP, leak and VT were measured with and without occlusion of the contralateral nostril using the Leoni ventilator (Heinen & Löwenstein, Germany) and a recently developed algorithm to correct measured VT in the presence of leaks. The measuring range of the Leoni is limited to leaks