Until recently no universally accepted clinical definition existed for the polycystic ovary syndrome (PCOS). What has emerged from research over the last 30 yr is a profound heterogeneity and ongoing speculation regarding etiology. The various symptoms and signs related to PCOS have now been extensively evaluated as to their possible contribution to the diagnosis. Consensus has been reached for the use of oligomenorrhea or amenorrhea, clinical or biochemical hyperandrogenism, and polycystic ovaries at ultrasound as key diagnostic criteria. Obesity, insulin resistance, and the so-called metabolic syndrome should be recognized as associated conditions that present long-term health risks for diagnosed PCOS cases. The way all these features need to be applied in the work up of the individual index patient is reviewed here.