Polycystic ovary syndrome (PCOS) is the commonest endocrinopathy affecting women of reproductive age, manifested with a variety of clinical signs, none of which is pathognomonic. The association of insulin resistance and reproductive abnormalities with clinical hyper-androgenism in a woman was first demonstrated by Achard and Thiers in the “diabetes of bearded woman.” The link of PCOS with insulin resistance was subsequently established by clinical studies characterizing the profound insulin resistance in obese and lean PCOS patients. Insulin resistance, hyperinsulinemia, and beta-cell dysfunction are very common in PCOS, but are not required for the diagnosis. The numerous in vivo and in vitro data supporting the central role of insulin resistance in the pathogenesis of PCOS found a broad clinical application in the management of the syndrome, where the regulation of cycle abnormalities and the facilitation of pregnancy in obese PCOS patients was assisted by co-administration of agents such as the well-known insulin sensitizers. The documentation of the presence of insulin resistance contributed substantially to unravel several metabolic components present in the syndrome. Today our knowledge about PCOS appers to have broader health implications and to have profoundly altered our view of the gravity of this condition.