Women with polycystic ovarian syndrome have chronic anovulation and androgen excess not attributable to another cause. This condition occurs in approximately 4% of women. The fundamental pathophysiologic defect is unknown, but important characteristics include insulin resistance, hyperandrogenism, and altered gonadotropin dynamics. Inadequate follicle-stimulating hormone is hypothesized to be a proximate cause of anovulation. Obesity frequently complicates polycystic ovarian syndrome but is not a defining characteristic. The diagnostic approach should be based largely on history and physical examination, thus avoiding numerous laboratory tests that don’t contribute to clinical management. Women with polycystic ovarian syndrome typically present because of irregular bleeding, hirsutism, and/or infertility. These conditions can be treated directly with oral contraceptives, oral contraceptives plus spironolactone, and ovulation induction, respectively. However, women with polycystic ovarian syndrome also have a substantially higher prevalence of diabetes and increased risk factors for cardiovascular disease. They should also be screened, therefore, for these conditions and followed closely if any risk factors are uncovered. For obese women with polycystic ovarian syndrome, behavioral weight management is a central component of the overall treatment strategy.