Sleep disturbances are associated with a number of diseases and mortality, and women complain more of disturbed sleep than men, and seek treatment more often. The reason for the differences is not clear, but stress is one proposed factor. However, apart from sleep complaints we know very little about the other aspects of sleep and gender, but we would expect to see sleep complaints reflected in objective sleep, as well as in sleep related: immune system activation, morbidity & sickness absence, fatigue, and mortality. Information on these influences is necessary for understanding the pattern of gender differences in sleep and to improve interventions. The project includes an objective sleep study (polysomnography, the “gold standard” of sleep measurement) in 800 men and women (half each), C-reactive protein (indicator of inflammation) from blood samples in the morning after the recording, fatigue ratings at 5 points during the day, a cognitive test and ratings of stress. It also includes the covariation of sleep, stress and sickness absence across 8 years (5000 participants) within genders, and a large (N=43000) epidemiological study of the prospective association between reported sleep problems and later morbidity and mortality –in relation to gender. This is a comprehensive and unique effort to understand gender related differences in sleep. An additional strength is that the same self-report sleep questionnaire is used in all three sub-studies.