Twenty-seven women referred to a sleep disorders clinic for symptoms of obstructive sleep apnea syndrome (OSAS) during one year were systematically analyzed after polygraphic monitoring of sleep and cephalometric x-ray examination. Our subjects, one-third of whom were premenopausal, comprised approximately 12 percent of the total OSAS population seen. Women with OSAS were compared with 110 OSAS men and with a group of 16 women without OSAS but referred to orthodontists for mild dental malocclusion. Women with OSAS were massively obese, much more so than their male counterparts. There was no significant difference between pre- and postmenopausal women, with the exception of the respiratory disturbance index (RDI), which was lower in the postmenopausal group despite similar morbid obesity (seemingly better tolerated by women with OSAS than by men with the same syndrome) and long mandibular plane-hyoid bone distance. The significantly higher RDI noted in premenopausal women, despite equally massive obesity and upper airway abnormalities, is thought to be related to hormonal status and better arousal response. Chronic obstructive lung disease (COLD) seen in a subgroup of women with OSAS did not differentiate this subgroup from the other OSAS patients when oxygen saturation during sleep, frequency of abnormal respiratory events and sleep variables were considered. Massive obesity is the dominant factor for the appearance of OSAS in women.