Summary Question Does oestrogen reduce the incidence of major disease in healthy post-menopausal women? Study design Double-blind randomised placebo controlled trial. Main results At 6.8 years, oestrogen significantly increased the risk of stroke by 39% compared with placebo. There were no significant differences in the rate of coronary heart disease between groups. Oestrogen decreased the risk of osteoporotic fractures by 30% in healthy post-menopausal women compared with placebo (see Results table). There were no significant differences in the incidence of breast cancer, venous thromboembolic disease, colorectal cancer, or death between groups. Authors’ conclusions Oestrogen had no effect on the risk of coronary heart disease, but significantly increased the risk of stroke in post-menopausal women. Women should be warned of this risk if they are considering oestrogen therapy.