It has been difficult to establish the association between mammary cancer and hormones utilized to control menopausal symptoms. However, recent studies allow us to dilucidate a higher risk in patients so treated. This relationship appears more evident with the combination of conjugated estrogens and medroxyprogesterone acetate. In evaluating therapy of hormonal replacement within the concept of causality, one finds that it fulfills several parameters, so as to include it as a causal factor in the development of mammary cancer.