Obesity is increasing worldwide and has a detrimental influence on female reproductive health. Particularly in obese women the hypothalamic-pituitary-ovarian axis is disrupted and they frequently suffer from menstrual dysfunction which eventually leads to anovulation and infertility. Majority of women with an ovulatory disorder contributing to their infertility have polycystic ovary syndrome (PCOS) and a significant proportion of women with PCOS are obese. The development of obesity in women with PCOS, in turn, amplifies and may even unmask the biochemical and clinical abnormalities characteristic of this condition. In obesity, the adipocytes act as an endocrine organ through secretion of adipokines that are commonly involved in metabolic regulation and inflammatory process. Additionally, hormonal imbalance such as insulin resistance and hyperandrogenism further contribute to fertility dysfunction. Overweight and obese women have lower outcomes following fertility treatments than the normal population. They poorly respond to induction of ovulation, require higher doses of gonadotropins and longer treatment courses for follicular development and ovulatory cycles. Weight loss is essential for the improvement of reproductive outcomes in obese women with and without PCOS. Women should be provided with assistance to lose weight, including psychological support, dietary advice, exercise classes and where appropriate, weight reducing agents or bariatric surgery.