OBJECTIVE: The polycystic ovary syndrome (PCOS) and the metabolic syndrome (MetS) are common disorders that share many characteristics, particularly abdominal obesity and insulin resistance. Our objective was to compare the prevalence of MetS between a large cohort of patients with PCOS and body mass index -matched controls.DESIGN: Cross-sectional study.PATIENTS: We studied 1223 patients with PCOS and 277 healthy women. Diagnosis of PCOS was based on the revised Rotterdam criteria. Women with PCOS were divided into those who fulfilled both the Rotterdam criteria and the diagnostic criteria of the 1990 National Institutes of Health definition of PCOS (group 1, n = 905) and into those with the additional phenotypes introduced by the Rotterdam criteria (group 2, n = 318). Diagnosis of MetS was based on four different definitions.MEASUREMENTS: Anthropometric, metabolic, hormonal and ultrasonographic features of PCOS.RESULTS: The prevalence of metabolic syndrome (MetS) was higher in women with PCOS than in controls when the National Cholesterol Education Program Adult Treatment Panel III definition of MetS was applied (15·8% and 10·1%, respectively; P = 0·021) but not with the three more recent MetS definitions. The prevalence of MetS was higher in group 1 than in controls regardless of the applied MetS definition. In contrast, the prevalence of MetS was similar in group 2 and in controls regardless of the applied MetS definition. In logistic regression analysis, PCOS did not predict the presence of MetS.CONCLUSIONS: Polycystic ovary syndrome per se does not appear to increase the risk of MetS independent of abdominal obesity.