A questionnaire study was carried out in 6000 randomly selected women in the County of Jämtland in Sweden. The response rate was 61.2%. Questions were asked about general health, height and body weight, sleep, menstruation and menopausal complaints. There were also questions about visits to doctors and the use of sleeping pills and hormone preparations. A deterioration of the night's sleep after the age of 60 years was associated especially with a low body mass index (BMI). In the subgroup with a BMI below 20 (kg m-2), frequent awakenings were reported 4 times more often in women 60-64 years old than in those aged 40-44 years. No such difference was found with a BMI > or = 30. In the age group 60-64 years twice as many women with BMI > or = 30 as women with BMI or = 30kg m-2.