The association (and similarities) of polycystic ovary syndrome with the metabolic syndrome, in which excessive (visceral) accumulation and insulin resistance are patho-physiologically linked suggests an important role for weight loss and weight loss maintenance both for symptom improvement and improved fertility in the short term, and reduced cardiovascular and metabolic risk over the patients lifetime. A number of studies have confirmed that in PCOS, dietary-induced weight reduction improves hyperlipidaemia, reduces insulin resistance, and increases SHBG concentration, so reducing biochemical hyperandrogenism and improving menstrual regularity, as well as fertility and reproductive outcome. Similarly to persons with type 2 diabetes, women with PCOS may be more resistant to weight loss and drop-out rates for diet interventions seem as high in women with PCOS as in the general obese population. A specific role or benefit for high protein or low glycaemic index diets has not been established. The insulin sensitising drugs such as metformin or thiazolinediones, or the anti-androgen flutamide, alone or in combination with lifestyle and diet interventions improves ovulation and fertility has little impact on body weight. This has led to calls that these drugs and ovulation induction drugs should not be used until weight loss has been achieved because of the worse outcome of pregnancy in obese women. There is little experience of specific anti-obesity drugs in PCOS, perhaps because none are approved for use in pregnancy. However one study showed that compared to metformin, the lipase-inhibitor orlistat produced greater weight loss, but similar reductions in testosterone. In 30 severely obese women with PCOS, bariatric surgery produced a mean 57% excess weight loss, resolution of diabetes in all 11 with the disease, resolution of menstrual abnormalities and 5 spontaneous conceptions. Weight management should form a key part of the management of PCOS.