To understand how body weight affects the menstrual cycle, it is first necessary to review the hormonal control of the normal functioning cycle. The menstrual cycle is influenced by body fat, and obesity can lead to irregularities in the menstrual cycle. Studies have indicated that 30-47% of obese women have irregular cycles,1,2 although the incidence of infertility among obese women is not that high. Infertility in this population seems to be related to ovulatory dysfunction. A large casecontrolled study that compared obese, anovulatory women with fertile controls found a relationship between BMI at age 18 and subsequent anovulatory infertility.