Obstructive sleep apnoea (OSA) is primarily regarded as a male disorder, presenting with snoring, daytime sleepiness and cardiovascular disease. We aimed to determine the frequency of sleep apnoea among females in the general population. We investigated 400 females from a population-based random sample of 10,000 females aged 20-70 yrs. They answered a questionnaire and performed overnight polysomnography. OSA (apnoea/hypopnoea index (AHI) ≥5) was found in 50% (95% CI 45-55%) of females aged 20-70 yrs. Sleep apnoea was related to age, obesity and hypertension, but not to daytime sleepiness. Severe sleep apnoea (AHI ≥30) was present in 14% (95% CI 8.1-21%) of females aged 55-70 yrs and in 31% (95% CI 12-50%) of obese females with a body mass index of ≥30 kg·m(-2) aged 55-70 yrs. Sleep apnoea with daytime sleepiness and sleep apnoea with hypertension were observed as two different phenotypes of OSA. OSA occurs in 50% of females aged 20-70 yrs. 20% of females have moderate and 6% severe sleep apnoea. Sleep apnoea in females is related to age, obesity and hypertension, but not to daytime sleepiness. When searching for sleep apnoea in females, females with hypertension or obesity should be investigated.