Sonography of the pelvis is warranted in virtually every potential PCOS patient. Evaluation should be performed by individuals experienced in judging ovarian and endometrial function. The finding of greater than ten (some say eight) cystic structures less than 10 mm in either ovary meets the generally established ultrasound criteria of PCOS. Often cysts of PCOS are located in a peripheral subcortical ring leading to the reference of a “string of pearls.” The PCOS ovaries are typically 1.5 to 3 times normal size. In some cases the ovary is virtually filled with small cysts. In other cases, it is heterogeneously dense with hardly detectable microcystic changes. It must be remembered that any hyperandrogenic state may be manifested by the PCO-appearing ovary. Diffusely enlarged ovaries without discrete mass on ultrasound are often associated with insulin resistance.