Although there has been considerable interest in the effects of nasal airway impairment on facial growth, the relationship is still unclear. This study examined the effect of nasal airway size on upper airway pressures during breathing. Three phases of data collection were involved. The first phase used a model to describe pressures during simulated normal and impaired respirations. The second phase involved subjects with normal airways, and the third used persons who were judged by an otolaryngologist to be nasally impaired. Aerodynamic assessment techniques were used to measure airway pressures during breathing and to assess nasal airway size. Results of the modeling study suggest that when nasal cross-sectional area is greater than 0.1 cm2, pressures associated with breathing are not excessive. These findings also suggest that slight lip opening (2 to 3 mm) would significantly reduce airway pressures. In addition, pressure magnitudes of the normal and nasally impaired groups were similar to the modeling data, and no significant difference in pressures was observed between the two groups. Accordingly, the assumptions that nasally impaired persons generate abnormal breathing pressures and that these pressures directly influence facial growth are questionable.