Most patients with sleep apnoea/hypopnoea syndrome (SAHS) are middle-aged men. As there are conflicting data on the effects of age and gender on upper airway calibre, we tested the hypothesis that increasing age and the male sex predispose to upper airway narrowing in normal subjects. We measured upper airway calibre using acoustic reflection in 60 men and 54 women (median 35, range 16-74 yrs) both seated and supine. All upper airway dimensions, except oropharyngeal junction (OPJ), decreased with increasing age in both men and women (r > -0.24, p < or = 0.05) while supine (r2 > 0.06). Men had greater changes in airway area at OPJ on lying down (mean (SEM) 0.5 (0.1), 0.2 (0.1) cm2; p < 0.02). Men had greater body mass indices (mean (SD) 26 (4), 24 (4) kg.m-2; p = 0.04), and larger neck circumferences (mean (SD) 38 (3), 33 (2) cm; p < 0.0001) than women. For any body mass index, neck circumference was larger in men than women (p < 0.001). This study shows that upper airway size decreases with increasing age in both men and women, and that men have greater upper airway collapsibility on lying down at oropharyngeal junction than women.