Chronic insomnia affects approximately 8-9% of the population. The prevalence of this disorder rises dramatically across the lifespan, especially so in women. When it is chronic, insomnia is associated with increased fatigue, cognitive impairment, mood disturbance, physical complaints, diminished quality of life and increased health care consumption. There is also more limited evidence (based on epidemiologic studies or experimental studies in healthy subjects) that insomnia and/or sleep loss may be a risk factor for hypertension and/or cardiovascular disease and increased mortality.