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 < 20 slept without waking up at night. BMI was similar in women with and without oestrogen therapy before the menopause. After the menopause the BMI in these two groups was 25.0 +/- 3.1 (mean +/- S.D.) and 25.6 +/- 3.8, respectively (P < 0.05). Oestrogen-treated women had fewer sleep disorders than other women of the same age. Of the premenopausal women, 3.4% used sleeping pills, compared with 8.0% after the menopause. Before the menopause the use of sleeping pills was not related to BMI, but after the menopause this use was twice as common among women with BMI < 20 kg m-2 than among those with BMI > or = 30kg m-2.