Our studies show that obese women with polycystic ovary syndrome are more likely to have hirsutism and menstrual disturbances than are lean women with PCOS. The most obvious biochemical differences between obese and lean women with PCOS is that SHBG concentrations are much lower in women with obesity. The SHBG levels are inversely related to insulin, and insulin has been shown to have a direct inhibitory action on SHBG secretion. Other factors, however, may contribute to the mechanism of the increased prevalence of hirsutism and anovulation in obese women with PCOS, such as a direct effect of insulin or increased activity of 5 alpha-reductase in peripheral tissues. Finally we have been able to show that weight reduction of more than 5% is associated with an improved biochemical profile and, importantly, with restoration of fertility.