Polycystic Ovary Syndrome is a heterogenous syndrome of unknown causation commonly associated with obesity. The particular timing of the onset of obesity may be important, since the earlier the onset of obesity the greater the severity of the metabolic and hormonal aberrations. Early postnatal life and peripubertal periods may be critical windows for the development of the "adiposity insult". The interaction of adiposity with genetic traits as well as with prenatal environmental factors may further aggravate the metabolic and endocrine abnormalities, which become more pronounced in adolescence.