Oestrogen replacement therapy (ORT) significantly increases the relative risk (RR) of endometrial cancer, especially long-term oestrogen use (RR: 9.5; 95% confidence interval (CI): 7.4-12.3). Addition of a progestin to ORT reduces this increased risk completely or largely. The risk of breast cancer is increased after ORT of 5 years or longer (RR: 1.23; 95% CI: 1.08-1.40). Addition of a progestin does not reduce this increased risk. The possibility cannot be excluded that long-term ORT increases the risk of epithelial ovarian cancer. No significant association between ORT and cervical cancer has been demonstrated. It is safe to prescribe ORT for a period shorter than 5 years for women with menopausal symptoms. Addition of a progestin is indicated when the uterus is in situ. Hormonal supplementation therapy is to be discouraged in women treated for breast cancer, may be considered in young women previously treated for endometrial or ovarian cancer with a good prognosis and severe menopausal symptoms and is justified in women previously treated for cervical cancer.