Polycystic ovary syndrome is the single most common endocrine abnormality of women of reproductive age and is a leading cause of female infertility. Common clinical features include hirsutism, various ovarian abnormalities, obesity, and insulin resistance. Expert consensus recommendations on diagnostic criteria vary, but the most recent focus on the presence of clinical features of hyperandrogenism, hyperandrogenemia, polycystic ovaries, and ovulatory and menstrual dysfunction to the exclusion of alternative diagnoses. In adolescence, diagnosis is more difficult because of the frequent presence of individual clinical findings in otherwise "normal" individuals. Laboratory tests and pelvic ultrasound are necessary to confirm polycystic ovary syndrome and exclude other disorders that may mimic this syndrome. Treatment is centered on the clinical manifestations and should be initiated early to prevent/limit long-term complications, including the metabolic syndrome, diabetes, endometrial carcinoma, and infertility.