Posture has a major effect on breathing during sleep. Snoring, hypopneas, and apneas are all more common lying than sitting and more common supine than in a lateral lying position. Because the effect of the lateral lying position on upper airway caliber has not previously been studied, we examined this in 20 normal awake subjects and also determined the effect of neck position. The acoustic reflection technique was used. Pharyngeal cross-sectional areas (CSA) fell significantly from the sitting to supine position (oropharyngeal junction, from 1.65 +/- [SEM] 0.6 cm to 1.31 +/- 0.07 cm), but there was no difference in CSA between the supine and lateral positions for oropharyngeal junction (1.36 +/- 0.06 cm), mean pharyngeal area, maximal pharyngeal area, or pharyngeal volume. Neck hyper-extension significantly increased pharyngeal CSA (e.g., oropharyngeal junction null position 1.51 +/- 0.08, hyper-extension 1.94 +/- 0.11 cm), but there was no significant effect of neck flexion on airway CSA. These results confirm that in normal awake subjects, pharyngeal areas are smaller lying than sitting but also showed no significant difference between CSA in the supine and lateral lying positions. The study also demonstrates that the upper airway caliber increases with neck extension in conscious adults.