Polycystic ovary syndrome (PCOS) is frequent during adolescence (prevalence ≈ 6 %), and the prevalence increases in obese or type 1 diabetic (T1D) adolescent girls. During puberty, PCOS diagnosis is difficult because of the overlap with some pubertal physiologic signs. The 2017 international consortium suggests two required diagnostic criteria: persistent menstrual disturbances and hyperandrogenism. PCOS physiopathology is complex, including interactions between genetic, epigenetic factors, primary ovarian abnormalities, neuroendocrine alterations, hormonal and metabolic factors. Insulin seems to have a central place in obese or T1D adolescent girls. The treatment is still debated and should be monitored according to the main symptoms.