In 1990 a group of experts under the auspices of the National Institutes of Health (NIH) considered affected by PCOS every woman with hyperandrogenism and chronic anovulation; after having excluded other specific diseases that mimic that clinic like Cushing's syndrome, androgen secreting tumors and congenital adrenal hyperplasia (NIH criteria). The presence of polycystic ovaries under ultrasound exploration was considered controversial criteria and was not included for diagnosis. In May 2003 a new committee of experts joined in Rotterdam under the auspice of the American Society for Reproductive Medicine (ASRM) and the European Society for Human Reproduction and Embryology (ESHRE), included polycystic ovaries by ultrasound to the physiologic abnormalities for diagnosis. Thus, diagnosis should include unless two of the following: oligo or anovulation; hyperandrogenism (clinic or biochemical) and polycystic ovaries under ultrasound examination.