The majority of male patients with obstructive sleep apnoea (OSA) have an abnormal pharyngeal structure and function, with episodic complete airway occlusion during sleep. Since OSA is less common in females than in males, it is possible that other abnormalities are active in female patients with OSA. Consequently, we measured pharyngeal area and its lung volume-related changes (LVRC) from functional residual capacity (FRC) to residual volume (RV) in overweight females, 14 with OSA and 14 without OSA. Pharyngeal areas were measured using the acoustic reflection technique. While there were no significant differences in pharyngeal area between the OSA and control groups at either FRC (mean +/- SD, 3.49 +/- 0.46 cm2 vs 3.08 +/- 0.63 cm2) or RV (2.86 +/- 0.47 cm2 vs 2.67 +/- 0.49 cm2), the reduction in pharyngeal area between FRC and RV was significantly greater in the OSA group (0.63 +/- 0.23 cm2 vs 0.33 +/- 0.32 cm2, p less than 0.05). Furthermore, although the expiratory reserve volume (ERV) was not significantly different between the two groups (0.4 +/- 0.2 l vs 0.4 +/- 0.3 l), LVRC, defined as the reduction in pharyngeal area normalized by ERV, was significantly higher in the females with OSA than in the non-apnoeic controls (2.68 +/- 2.24 cm2.l-1 vs 1.17 +/- 1.23 cm2.l-1, p less than 0.02). We conclude that females with OSA have abnormal pharyngeal mechanics similar to males with OSA.