['To evaluate the contribution to glucose intolerance and metabolic syndrome of obesity combined with the diagnostic criteria of polycystic ovary syndrome (PCOS).', 'Prospective study.', 'University teaching hospital from 31 August 2010 to 31 August 2011.', 'Two hundred and twenty women with PCOS and seventy normal control women.', 'The clinical and biochemical characteristics of women with PCOS and control women were evaluated. Main outcome measures. The impact of obesity, hyperandrogenism, oligo-anovulation and polycystic ovary morphology on impaired glucose tolerance and metabolic disturbances.', 'Obese women with PCOS had significantly higher insulin resistance than obese normal control women. Logistic regression analysis showed that obesity was the only factor that predicted impaired glucose tolerance and metabolic syndrome. Use of the area under the receiver operating characteristic curve (AUROC) for the body mass index to predict impaired glucose tolerance and metabolic syndrome was more accurate than AUROCs for serum total testosterone level and the average menstrual interval.'] Is obesity the predominant predictor of impaired glucose tolerance and metabolic disturbance in polycystic ovary syndrome?