Polycystic ovary syndrome (PCOS) is the most common endocrinopathy in women, typically presenting with menstrual irregularities and signs of androgen excess. Approximately 4-10% of reproductive aged women have PCOS. The fact that PCOS often presents in adolescence and the chance of long-term adverse health consequences indicate the need for early diagnosis and intervention. Menstrual dysfunction and hyperandrogenism are key features of the diagnosis of PCOS in reproductive aged women. Diagnosis can be challenging, however, in adolescent girls. The etiology of PCOS is complex and incompletely understood. Therapy should focus on alleviating symptoms and preventing adverse health consequences.