We conducted a study with the objective of comparing the performance of two different systems for patient-triggered ventilation in neonates (impedance versus flow/volume-triggered) by measuring response time, autotrigger and trigger failure rates, ventilation, and gas exchange. The two ventilator systems were applied in random order in 10 preterm neonates (median gestational age: 30.5 wk; range: 27 to 34 wk; body weight: 1,266 g; range: 840 to 2,240 g) using identical ventilator settings. The median (range) response time was 169 (98 to 305) ms for the impedance system and 115 (79 to 184) ms for the flow/volume system (p < 0.01). The longer and more variable response time of the impedance system was secondary to a phase lag of the impedance signal caused by chest wall distortion. Although 13.1 (0.2 to 29.4)% of mechanical breaths were autotriggered with the impedance system, there were no autotriggered breaths using the flow/volume system (p < 0.01). The rate of trigger failures was not significantly different with the two systems, at 1.2 (0 to 4.4)% (impedance) versus 3.1 (0 to 6.4)% (flow/volume). Minute ventilation was smaller with the impedance system (p < 0.001), because of the larger number of breaths triggered late in inspiration or during expiration. We conclude that the flow/volume-triggered system is less prone to autotriggering and has a shorter and more consistent response time than the impedance-triggered system. The impedance-triggered system is more susceptible to artifacts and chest wall distortion.