The differential diagnosis and clinical management of abnormal uterine bleeding and of amenorrhea present complex challenges to the provider of well woman gynecologic care. The physiologic origins of these problems are detailed and related to historical information, possible physical findings, and laboratory tests results. In particular, dysfunctional uterine bleeding is distinguished from other causes of bleeding such as infections, carcinoma, ectopic pregnancy, side effects of contraception, and benign disorders such as myomas. The differential diagnosis of amenorrhea is also presented with attention to medical and exogenous causes, as well as amenorrhea due to alterations of hypothalamic function; pituitary, ovarian, thyroid, and adrenal dysfunction; and abnormalities of the outflow tract. Strategies are presented for initiating the clinical investigation of these problems, when to comanage with a gynecologist, and when to refer.