Respiratory system compliance (C_RS) in infants with cystic fibrosis (CF) has been reported as decreased or not different compared to healthy controls; however, the reported measurements of C_RS were "quasi=static" or by the single occlusion technique with all measurements limited to tidal lung volume, as well as using inspiratory rather than expiratory pressures. We compared the passive elastic properties of the respiratory system of sleeping infants with CF (N = 10) and Healthy Controls (N = 34) by measuring static deflation pressure volume (PV) curves from a lung volume at 30 cmH₂O (V₃₀) to functional residual capacity. There was no significant difference between the groups for C_RS, which was measured as the slope between airway relaxation pressures of 5 and 15 cmH₂O, the linear portion of the deflation PV curve. In addition, when PV curves were normalized to V₃₀, there were no differences between the CF and Healthy Controls in the fractional volumes at any airway pressure. The CF infants had significantly lower forced expiratory flows; however, lower flows did not correlate with fractional volumes measured from the PV curve. Our findings indicate CF infants have normal elastic properties of the respiratory system.