Polycystic ovary syndrome Polycystic ovary syndrome (PCOS) is a health problem that affects 1 in 10 women of childbearing age. Women with PCOS have a hormonal imbalance and metabolism problems that may affect their overall health and appearance. PCOS is also a common and treatable cause of infertility. What is polycystic ovary syndrome (PCOS)? Polycystic ovary syndrome (PCOS), also known as polycystic ovarian syndrome, is a common health problem caused by an imbalance of reproductive hormones. The hormonal imbalance creates problems in the ovaries. The ovaries make the egg that is released each month as part of a healthy menstrual cycle. With PCOS, the egg may not develop as it should or it may not be released during ovulation as it should be. PCOS can cause missed or irregular menstrual periods. Irregular periods can lead to: Infertility (inability to get pregnant). In fact, PCOS is one of the most common causes of infertility in women. Development of cysts (small fluid-filled sacs)