Polycystic Ovary Syndrome (PCOS) is recognized as the most common endocrine disorder of reproductive-aged women around the world. This document, produced by the collaboration of the American Association of Clinical Endocrinologists (AACE) and the Androgen Excess and PCOS Society (AES) aims to highlight the most important clinical issues confronting physicians and their patients with PCOS. It is a summary of current best practices in 2015. PCOS has been defined using various criteria, including menstrual irregularity, hyperandrogenism, and polycystic ovary morphology (PCOM). General agreement exists among specialty society guidelines that the diagnosis of PCOS must be based on the presence of at least two of the following three criteria: chronic anovulation, hyperandrogenism (clinical or biological) and polycystic ovaries. There is need for careful clinical assessment of women's history, physical examination, and laboratory evaluation, emphasizing the accuracy and validity of the methodology used for both biochemical measurements and ovarian imaging. Free testosterone (T) levels are more sensitive than the measurement of total T for establishing the existence of androgen excess and should be ideally determined through equilibrium dialysis techniques. Value of measuring levels of androgens other than T in patients with PCOS is relatively low. New ultrasound machines allow diagnosis of PCOM in patients having at least 25 small follicles (2 to 9 mm) in the whole ovary. Ovarian size at 10 mL remains the threshold between normal and increased ovary size. Serum 17-hydroxyprogesterone and anti-Müllerian hormone are useful for determining a diagnosis of PCOS. Correct diagnosis of PCOS impacts on the likelihood of associated metabolic and cardiovascular risks and leads to appropriate intervention, depending upon the woman's age, reproductive status, and her own concerns. The management of women with PCOS should include reproductive function, as well as the care of hirsutism, alopecia, and acne. Cycle length >35 days suggests chronic anovulation, but cycle length slightly longer than normal (32 to 35 days) or slightly irregular (32 to 35-36 days) needs assessment for ovulatory dysfunction. Ovulatory dysfunction is associated with increased prevalence of endometrial hyperplasia and endometrial cancer, in addition to infertility. In PCOS, hirsutism develops gradually and intensifies with weight gain. In the neoplastic virilizing states, hirsutism is of rapid onset, usually associated with clitoromegaly and oligomenorrhea. Girls with severe acne or acne resistant to oral and topical agents, including isotretinoin (Accutane), may have a 40% likelihood of developing PCOS. Hair loss patterns are variable in women with hyperandrogenemia, typically the vertex, crown or diffuse pattern, whereas women with more severe hyperandrogenemia may see bitemporal hair loss and loss of the frontal hairline. Oral contraceptives (OCPs) can effectively lower androgens and block the effect of androgens via suppression of ovarian androgen production and by increasing sex hormone-binding globulin. Physiologic doses of dexamethasone or prednisone can directly lower adrenal androgen output. Anti-androgens can be used to block the effects of androgen in the pilosebaceous unit or in the hair follicle. Anti-androgen therapy works through competitive antagonism of the androgen receptor (spironolactone, cyproterone acetate, flutamide) or inhibition of 5α-reductase (finasteride) to prevent the conversion of T to its more potent form, 5α-dihydrotestosterone. The choice of antiandrogen therapy is guided by symptoms. The diagnosis of PCOS in adolescents is particularly challenging given significant age and developmental issues in this group. Management of infertility in women with PCOS requires an understanding of the pathophysiology of anovulation as well as currently available treatments. Many features of PCOS, including acne, menstrual irregularities, and hyperinsulinemia, are common in normal puberty. Menstrual irregularities with anovulatory cycles and varied cycle length are common due to the immaturity of the hypothalamic-pituitary-ovarian axis in the 2- to 3-year time period post-menarche. Persistent oligomenorrhea 2 to 3 years beyond menarche predicts ongoing menstrual irregularities and greater likelihood of underlying ovarian or adrenal dysfunction. In adolescent girls, large, multicystic ovaries are a common finding, so ultrasound is not a first-line investigation in women <17 years of age. Ovarian dysfunction in adolescents should be based on oligomenorrhea and/or biochemical evidence of oligo/anovulation, but there are major limitations to the sensitivity of T assays in ranges applicable to young girls. Metformin is commonly used in young girls and adolescents with PCOS as first-line monotherapy or in combination with OCPs and anti-androgen medications. In lean adolescent girls, a dose as low as 850 mg daily may be effective at reducing PCOS symptoms; in overweight and obese adolescents, dose escalation to 1.5 to 2.5 g daily is likely required. Anti-androgen therapy in adolescents could affect bone mass, although available short-term data suggest no effect on bone loss.