Adenomyosis has been an entity of some interest for many years, but little is known today of its pathogenesis. There is almost universal agreement that it is associated with an accentuation of the myometrial muscle pattern, multiparity, and endometrial hyperplasia. Some authors suggest that the myometrium is vulnerable to invasion by endometrial hyperplasia. Others postulate that the myometrium is vulnerable to invasion by endometrial glands because of the absence of a basement membrane. Women in the fourth and fifth decades of life are most commonly afflicted. Preoperative diagnosis is not common.