In a large prospective study carried out in the United Kingdom, the death-rate from diseases of the circulatory system in women who had used oral contraceptives was five times that of controls who had never used them; and the death-rate in those who had taken the pill continuously for 5 years or more was ten times that of the controls. The excess deaths in oral-contraceptive users were due to a wide range of vascular conditions. The total mortality-rate in women who had ever used the pill was increased by 40%, and this was due to an increase in deaths from circulatory diseases of 1 per 5000 ever-users per year. The excess was substantially greater than the death-rate from complications of pregnancy in the controls, and was double the death-rate from accidents. The excess mortality-rate increased with age, cigarette smoking, and duration of oral contraceptive use.