Adenomyosis uteri is a common gynaecological disorder that is characterized by the presence of ectopic endometrial glands and stroma in the myometrium. Although adenomyosis and endometriosis are different diseases, both of them grow and regress in an oestrogen-dependent fashion. Polymorphisms in the oestrogen receptor alpha gene are associated with a risk of adenomyosis. Adenomyotic tissue contains steroid receptors as well as aromatase and sulphatase enzymes. Together with the circulating oestrogen, locally produced oestrogens stimulate the growth of tissue mediated by the oestrogen receptors. Oestrogen metabolism, including the expression pattern of aromatase and the regulation of 17beta-hydroxysteroid dehydrogenase type 2 is altered in the eutopic endometrium of women with endometriosis, adenomyosis, and/or leiomyomas compared to that in the eutopic endometrium of women without disease. In addition to the conventional hormonal treatment with gonadotropin-releasing hormone agonists and danazol, the use of steroid-releasing intrauterine devices may be applicable to clinics.