Context: Polycystic ovary syndrome (PCOS) and the metabolic syndrome have many features in common and may share the same pathogenesis. Objective: This study was performed to determine the prevalence and predictors of the metabolic syndrome in PCOS. Design: The clinical, hormonal, and oral glucose tolerance test results were analyzed in 394 PCOS women who were screened for participation in a multicenter trial to evaluate the effects of troglitazone on ovulation and hirsutism. Setting: A multicenter clinical trial is presented. Patients or Other Participants: The subjects were women with PCOS who had or lacked the metabolic syndrome. Main Outcome Measures: Waist circumference, fasting glucose, high-density lipoprotein cholesterol and triglyceride concentrations, and blood pressure were the main outcome measures. Results: Twenty-six (6.6%) subjects had diabetes; among the 368 nondiabetics, the prevalence for individual components comprising the metabolic syndrome were: waist circumference greater than 88 cm in 80%, high-density lipoprotein cholesterol less than 50 mg/dl in 66%, triglycerides greater than or equal to 150 mg/dl in 32%, blood pressure greater than or equal to 130/85 mm Hg in 21%, and fasting glucose concentrations greater than or equal to 110 mg/dl in 5%. Three or more of these individual criteria were present in 123 (33.4%) subjects overall. The prevalence of the metabolic syndrome did not differ significantly between racial/ethnic groups. The prevalence of the metabolic syndrome from lowest to highest quartile of free testosterone concentration was 19.8, 31.3, 46.9, and 35.0%, respectively [P = 0.056 adjusted for body mass index (BMI)]. None of the 52 women with a BMI less than 27.0 kg/m2 had the metabolic syndrome; those in the top BMI quartile were 13.7 times more likely (95% confidence interval, 5.7-33.0) to have the metabolic syndrome compared with those in the lowest quartile. Thirty-eight percent of those with the metabolic syndrome had impaired glucose tolerance compared with 19% without the metabolic syndrome (P < 0.001). Conclusions: The metabolic syndrome and its individual components are common in PCOS, particularly among women with the highest insulin levels and BMI. Hyperinsulinemia is a likely common pathogenetic factor for both PCOS and the metabolic syndrome. Copyright © 2006 by The Endocrine Society.