Objective: To describe the frequency and type of patient-ventilator asynchrony in mechanically ventilated children by analyzing ventilator flow and pressure signals. Design: Prospective observational study. Setting: Tertiary PICU in a university hospital. Patients: Mechanically ventilated children between 0 and 18 years old and who were able to initiate and maintain spontaneous breathing were eligible for inclusion. Patients with congenital or acquired neuromuscular disorders, those with congenital or acquired central nervous system disorders, and those who were unable to initiate and maintain spontaneous breathing from any other cause were excluded. Interventions: None. Measurements and Main Results: All patients were ventilated in a time-cycled, pressure-limited mode with flow triggering set at 1.0 L/min by using the Evita XL (Drager, Lubeck, Germany). Patient-ventilator asynchrony was identified by a random 30-minute continuous recording and an offline analysis of the flow and pressure signals. Patient-ventilator asynchrony was categorized and labeled into four different groups: 1) trigger asynchrony (i.e., insensitive trigger, double triggering, autotriggering, or trigger delay), 2) flow asynchrony, 3) termination asynchrony (i.e., delayed or premature termination), and 4) expiratory asynchrony. Flow and pressure signals were recorded in 45 patients for 30 minutes. A total number of 57,651 breaths were analyzed. Patient-ventilator asynchrony occurred in 19,175 breaths (33%), and it was seen in every patient. Ineffective triggering was the most predominant type of asynchrony (68%), followed by delayed termination (19%), double triggering (4%), and premature termination (3%). Patient-ventilator asynchrony significantly increased with lower levels of peak inspiratory pressure, positive end-expiratory pressure, and set frequency. Conclusions: Patient-ventilator asynchrony is extremely common in mechanically ventilated children, and the predominant cause is ineffective triggering.