Polycystic ovary syndrome (PCOS) is a very common disorder, affecting at least 6-8% of women in the reproductive age. Interestingly, a large body of evidence suggests PCOS is also a metabolic disease, with potential increase of cardiovascular risk. Several data indicate that up to 50-70% of PCOS subjects are insulin resistant, and it was hypothesized they may have specific abnormalities responsible for the impairment of insulin action. Insulin resistance is a well established pathogenic factor for type 2 diabetes mellitus. In addition, beta-cell dysfunction has been also reported in these women. Based on these findings, it is not surprising that abnormalities of glucose metabolism are considered a common feature of PCOS and that several scientific societies have identified PCOS as a significant nonmodifiable risk factor for DM. Nevertheless, literature on this issue is still limited. This paper review available evidence on this topic.