Polycystic ovarian syndrome (PCOS) is a heterogeneous diso-
rder characterized by disruption of the regular processes leading to ovulation. It is associated with hyperandrogenemia, normal or elevated luteinizing hormone (LH) secretion, and a raised LH-to-follicle stimulating hormone (FSH) ratio. Hyperandrogenemia in PCOS could be due simply to increased number of follicles or theca cell hyperplasia. Both insulin and insulin-like growth factors have been demonstrated to potentate the actions of LH on theca androgen production. Ultrasonography is the most sensitive diagnostic study in PCOS. Ultrasonogr-
aphic criteria for establishing the diagnosis of PCOS include 10 or more cysts that are 2-8 mm in diameter and are peripherally located around an echodense stroma. This paper presents an overview of PCOS epidemiological, clinical and diagnostic data, with an emphasis on sonographic appearance of this syndrome and the role of US in PCOS diagnostics.