Polycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility. Women with PCOS are at higher risk for several conditions, including metabolic syndrome, type 2 diabetes, cardiovascular disease, obesity, obstructive sleep apnea, mood disorders, endometrial hyperplasia, and endometrial cancer. The NICHD has supported research on the possible causes of PCOS and treatments for this problem for several decades. The NICHD is continuing its efforts to learn more about this far-reaching condition. Currently, NICHD-supported research is exploring genetic causes of PCOS, precursors or predictors of PCOS in adolescents, the development of animal models of PCOS, and new treatment strategies for this disorder.