Polycystic ovary syndrome (PCOS) is a heterogeneous endocrinologic disorder that is characterized by oligomenorrhea or amenorrhea and signs of hyperandrogenism. The cause of PCOS remains unknown, but the syndrome is associated with insulin resistance that in turn leads to hyperandrogenism. An accurate and prompt diagnosis of PCOS is important to understanding an adolescent's risk. In adolescents, both oligoovulation and hyperandrogenism are needed for the diagnosis of PCOS and ultrasound is not recommended. Lifelong health consequences of PCOS are significant and include obesity, diabetes, metabolic syndrome, and anovulatory infertility. The symptoms of PCOS can be disturbing to an adolescent girl.