Adolescent PCOS is characterized by menstrual cycle irregularities, usually less than 6 per year and with clinical or/and biochemical features of hyperandrogenism. Metabolic syndrome is seen in more than 50% of the cases with PCOS. It includes obesity, insulin resistance, dyslipidemia and hypertension. There is described a correlation between PCOS, precocious puberty and low birth weight. An important fact is that although PCOS is a very well known condition, its diagnosis in puberty is quite complicated. This is due to the heterogeneity of the syndrome in complex with the mild differences between PCOS and some physiologic processes in adolescence. The precise diagnosis is crucial for the exact therapy.