We have known for many years that oestrogen causes the most common type of endometrial cancer (type 1, sometimes described as oestrogen-dependent) and, for this reason, women with an intact uterus are not normally prescribed unopposed oestrogen therapy. Similarly, the positive association between obesity and type 1 endometrial cancer and the strong protective effects of pregnancy and the contraceptive pill are well established. In contrast, other types of endometrial cancer have been labelled as non-oestrogen-dependent with the assumption they are less sensitive to hormonal exposures. Cancers of the ovary (and fallopian tube and peritoneum) are, histologically, very similar to endometrial cancers and, although the same strong protective effects are seen for pregnancy and the contraceptive pill, they have not been associated with menopausal oestrogen therapy or obesity to the same extent as endometrial cancer. There is also a marked contrast between the strong protective effects seen for combinations of an oestrogen plus progestin taken in the form of oral contraceptives during the reproductive years, and the effects of oestrogen plus progestin menopausal hormone therapy. Furthermore, the effects of these hormones on the breast are often opposite to what is seen for endometrial and ovarian cancers. This presentation will discuss the relationships between exogenous oestrogens and progestins, factors that affect endogenous hormone levels and risks of ovarian and endometrial cancer and will compare and contrast these associations with those seen for breast cancer. It will also consider the potential effects of changing trends in obesity and contraceptive and menopausal hormone use on future rates of these cancers.