Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. The presentation is diverse. There is no single, unified definition of PCOS, no single diagnostic test and no consensus on the diagnostic criteria. Currently, PCOS is most commonly defined by the 2003 Rotterdam criteria, which requires at least two of three features for diagnosis--chronic anovulation, clinical and/or biochemical signs of hyperandrogenism, or polycystic ovaries. The aetiology is unknown, but the principal underlying disorder is thought to be reduced insulin sensitivity in peripheral tissue, and hence hyperinsulinaemia (high levels of insulin in the blood). Some affected women may have hyperandrogenism and polycystic ovaries with normal ovulatory function; however, like women with classic PCOS, they still have an increased risk of type 2 diabetes and cardiovascular events. Some women with PCOS have no symptoms or signs and live a normal life with normal childbearing status, but it is very difficult to predict which cases will follow this pattern. It is important to investigate women with menstrual irregularity when they first present, because they might have mild PCOS, which could otherwise be missed. It is therefore essential to educate the public, nurses and other healthcare professionals to identify affected women, so that strategies can be put in place to avoid or minimize the complications and consequences of PCOS.