Polycystic ovary syndrome is frequently associated with obesity, with at least 50% of women with polycystic ovary syndrome demonstrating overweight or obesity defined by body mass index >25 or >30 kg/m2. Overweight and obesity impact the clinical reproductive and metabolic features of the syndrome. Long-term complications of obesity such as cardiovascular risk and diabetes, as well as those over the short term in reproductive function, are significantly improved by lifestyle modification. Weight reduction is difficult to achieve over the long-term and programs designed for modest reduction in overall body weight (5% to 10%) with improvements in fitness are as effective as severe weight reduction in reducing metabolic disease and improving ovulatory potential. Further research is needed into the best approach for successful interventions that result in long-term sustained weight loss.