Among 118 patients with occlusive sleep apnea syndrome (OSA), defined as daytime hypersomnolence and an apnea hypopnea index (AHI) greater than ten events/h, 41 women were compared with 77 men. Body mass index, spirometric study, PaO2, PaCO2, and results from nocturnal polysomnography were examined in a two-way analysis of variance (ANOVA) for the effects of sex, age group, and a sex-age group interaction. The age groups examined were above and below 42 years, the breakpoint for menopause in the women. Younger persons tended to be more obese and to have a higher AHI. Both sexes had similar pulmonary function, AHI, and nocturnal desaturation, but women experienced significantly fewer completely occluded breathing events and had apneas of shorter mean and maximum duration than men of similar ages. No effect of menopausal status per se was observed. In OSA patients, differences in upper airway occlusion and apnea duration suggest differences between the sexes in upper airway physiology or respiratory control.