The prevalence of clinically relevant, obstructive sleep apnoea syndrome (OSAS) in the general population is 2% in women and 4% in men. With increasing age and onset of postmenopausal status, the prevalence of OSAS in women becomes comparable to that of males. However, compared to prevalence data, women are under-represented in clinical sleep laboratories. The present overview deals with the potential reasons for clinical under-recognition of OSAS in women. The fact that OSAS frequency is underestimated in women probably derives from the atypical clinical symptoms, dominated by difficulties of initiating and maintaining sleep and by a depressive mood. There are several protecting mechanisms in women that prevent or postpone OSAS development to higher age groups or until the onset of menopause. These factors include craniofacial morphology and function, gender-specific body-fat distribution and hormonal influences on ventilation and dilating muscles in the oropharynx. Physicians should be aware of the presence of sleep-disordered breathing in women and of their special features.