The symptoms of women with polycystic ovary syndrome (PCOS) include hirsutism and irregular menstrual bleeding due to ovarian androgen excess and chronic anovulation. Typically, these features emerge late in puberty or shortly thereafter. The proposed mechanism(s) responsible for increased ovarian androgen production include heightened theca cell responsiveness to gonadotropin stimulation, increased pituitary secretion of luteinizing hormone, and hyperinsulinemia. The cause of ovulatory dysfunction is not well understood, but is linked to abnormal follicle growth and development within the ovary. As a result, infertility is common among women with PCOS and, in many instances, is the initial presenting complaint. Insulin resistance and obesity are frequently associated with PCOS and probably contribute to the severity of symptoms. The polycystic ovary that accompanies the syndrome has recently been defined as having 12 or more follicles per ovary or an ovarian volume greater than 10 ml as determined by ultrasonography. In addition, there is an increased number of growing follicles in the polycystic ovary. Despite this distinctive appearance, the cause and development of the polycystic ovary are completely unknown.