Polycystic ovarian syndrome (PCOS) is a condition that is present in 5-6% of women of reproductive age. It has potentially profound implications for women with regard to anovulatory infertility and symptoms related to elevated androgen levels. In addition, in later life women are prone to significant health problems related to hyperinsulinaemia, with an excess risk for diabetes and cardiovascular risk factors. Evidence suggests that the adverse features of PCOS can be ameliorated with lifestyle intervention, such as diet and exercise, while further short-term benefits related to ovulation and cardiac risk factors may be derived from medication with metformin. Evidence for the long-term use of metformin to protect against adverse cardiovascular outcomes and for the use of metformin throughout pregnancy to reduce the risk of miscarriage, gestational diabetes, pre-eclampsia and fetal macrosomia is still lacking.