Polycystic ovary syndrome (PCOS) is usually defined clinically by hyperandrogenism and anovulation. Hyperinsulinaemia and insulin resistance are prominent features both in obese and nonobese women with PCOS, the latter having been shown to be more insulin resistant and hyperinsulinaemic than age- and weight-matched normal women. There is now a substantial body of evidence implicating hyperinsulinaemia in the pathogenesis of this disorder.