Health care providers who supply primary care to women will at some time encounter a patient presenting with symptoms of abnormal uterine bleeding and secondary dysmenorrhea. Adenomyosis, an elusive uterine disease, is a frequently ignored causative factor of these symptoms. Adenomyosis is considered a benign uterine condition in which the endometrial glands embed into the myometrium of the uterus. It is usually found in multiparous, middle-aged women who present with heavy, painful, cyclical bleeding associated with menstruation. This article addresses the incidence, etiology, symptomatology, and treatment modalities for adenomyosis. Implications for health care providers are discussed.