Adenomyosis is defined by the presence of endometrial mucosa within the myometrium. This probably occurs by invagination of the basalis endometrium into the myometrium. The process of invagination and intramyometrial spreading may be facilitated by the non-cyclic, anti-apoptotic activity of the basalis associated with relative hyper-oestrogenic states. Most cases of adenomyosis are discovered in multiparous women during the 'transitional' years (40-50 years), and the condition is associated with menorrhagia, dysmenorrhoea, endometrial polyps and leiomyomata uteri. Endometrioid adenocarcinoma is often associated with adenomyosis, is frequently of early stage and low histological grade, is hormone-sensitive, and has an excellent prognosis. Extension of malignant growth into foci of adenomyosis has no adverse effect on prognosis. Definite diagnosis and treatment of adenomyosis are obtained by hysterectomy. Although adenomyotic endometrial glands are hormone-sensitive, exogenous progestogenic agents are ineffective for the treatment of adenomyosis. Anti-oestrogenic danazol and gonadotrophin-releasing hormone (GnRH) analogues induce suppression of adenomyosis, but their use must be of short duration. Surgical extirpation, therefore, is the best therapeutic option.