Insulin resistance is present in women with PCOS. Women with PCOS are at high risk for developing type 2 diabetes, presumably due to the insulin resistance that accompanies the syndrome. Some actions of insulin may be effected by putative inositolphosphoglycan (IPG) mediators of insulin action, and evidence suggests that a deficiency in a specific D-chiro-inositol (DCI)-containing IPG may contribute to insulin resistance in individuals with impaired glucose tolerance or type 2 diabetes mellitus. A deficiency in DCI may also contribute to the insulin resistance in women with PCOS. In PCOS, three separate studies have shown that administration of DCI, the precursor to DCI-IPG, to women with PCOS improved glucose intolerance while reducing circulating insulin, improved ovulatory function, and decreased serum androgens. Serum triglycerides, HDL cholesterol and blood pressure improved in some of the studies as well. Collectively, these findings strongly suggest that administration of DCI improved insulin sensitivity in women with PCOS, and that a deficiency in DCI may contribute to the insulin resistance of this disorder.