Objective To assess the effect of the prone position on physiological measures, including inspiratory effort, metabolic cost of breathing, and neural drive to the diaphragm as compared with the supine position in infants with severe bronchiolitis requiring noninvasive ventilation. Study design Fourteen infants, median age 33 days (IQR [first and third quartiles], 25-58) were randomized to receive 7 cmH2O continuous positive airway pressure for 1 hour in the prone position or in the supine position, which was followed by cross-over to the supine position and the prone position for 1 hour, respectively. Flow, esophageal, airway, gastric, and transdiaphragmatic pressures, as well as electrical activity of the diaphragm were simultaneously recorded. The modified Wood clinical asthma score was also assessed. Results Median esophageal pressure-time product per minute was significantly lower in the prone position than in the supine position (227 cmH2O*s/minute [IQR, 156-282] cmH2O*s/minute vs 353 cmH2O*s/minute [IQR, 249-386 cmH2O*s/minute]; P?=?.048), as were the modified Wood clinical asthma score (P?=?.033) and electrical activity of the diaphragm (P?=?.006). The neuromechanical efficiency of the diaphragm, as assessed by transdiaphramagtic pressure to electrical activity of the diaphragm swing ratio, was significantly higher in the prone position than in the supine position (1.1 cmH2O/µV [IQR, 0.9-1.3 cmH2O/µV] vs 0.7 cmH2O/µV [IQR, 0.6-1.2 cmH2O/µV], respectively; P?=?.022). Conclusions This study suggests a benefit of the prone position for infants with severe bronchiolitis requiring noninvasive ventilation by significantly decreasing the inspiratory effort and the metabolic cost of breathing. Further studies are needed to evaluate the potential impact of these physiological findings in a larger population. Trial registration Clinicaltrials.gov: NCT02602678.