Sex hormones appear to play an important role in the lung health of women. This is, however, poorly understood and, in most aspects, poorly investigated; and the literature has been contradictory and confusing. This review presents recent research concerning the involvement of sex hormones in respiratory health of adult women, using the population surveys European Community Respiratory Health Survey and Respiratory Health in Northern Europe. Respiratory health varied substantially according to hormonal and metabolic conditions. First, menopause was associated with lower lung function and more respiratory symptoms, especially among lean women. Second, hormonal replacement therapy (HRT) was associated with increased risk for asthma and wheeze; also, this association was particularly strong among lean women. Third, women with irregular menstruations in fertile age had more asthma, particularly allergic asthma, and reduced lung function, independently of body mass index (BMI) and physical activity. The findings were consistent across cultural and geographical borders. Our studies revealed that considering interplay between hormonal and metabolic factors is a clue to understand the effects of female sex hormones on the airways. A BMI of around 24-25 kg/m(2) appeared to be optimal; women with this BMI had no increase in respiratory health problems when reaching menopause or using HRT, and women in fertile age with this BMI had optimal lung function independently of menstrual status. In conclusion, female sex hormones appear to play a most important role for lung health in women. Further research on effects of sex hormones on the airways should take into account potential interplay with metabolic factors.