The purpose of this analysis was to determine to what extent the clinical criteria for metabolic syndrome (MetSyn) proposed by the World Health Organization (WHO), the European Group for Study of Insulin Resistance (EGIR), the National Cholesterol Education Program Adult Treatment Panel III (ATP III), and the International Diabetes Foundation (IDF); triglyceride (TG)/high-density lipoprotein cholesterol (HDL-C) ratio >/=3.0; and enlarged waist circumference (>/=88 cm) and elevated TG (>/=129 mg/dL) (EWET) identified similar or different overweight women and, secondarily, to examine the effect of 7% weight reduction on MetSyn status. Metabolic syndrome was determined among 256 premenopausal women (age = 41 +/- 6 years, body mass index [BMI] = 32 +/- 4 kg/m(2)) participating in a dietary weight loss clinical trial based on the clinical criteria proposed by WHO, EGIR, ATP III, and IDF. The prevalence of TG/HDL-C ratio >/=3.0 and EWET was determined and compared with MetSyn status. Based on the clinical criteria, 16.1% (EGIR), 20.7% (WHO), 31.0% (ATP III), and 31.8% (IDF) of participants met the criteria for MetSyn; 30.3% and 31.8% had TG/HDL-C >/=3.0 and EWET, respectively. Between 77% and 99% of participants were similarly classified across the clinical criteria. The highest and lowest agreements were between ATP III and IDF (kappa = 0.98; 95% confidence interval, 0.96-1.0) and WHO and IDF (kappa = 0.39; 95% confidence interval, 0.26-0.51), respectively. The TG/HDL-C ratio >/=3.0 and EWET moderately agreed with all 4 clinical criteria for MetSyn (kappa range, 0.36-0.59). Among those diagnosed with MetSyn at baseline, 64.0% to 75.0% of the participants who lost >/=7% and 25.8% to 55.6% of participants who lost <7% of their baseline body weight in 6 months no longer met the various clinical criteria for MetSyn, TG/HDL-C >/=3.0, or EWET. Our findings indicate that MetSyn varies substantially between clinical criteria, which raise questions about the clinical utility of these criteria. Regardless of MetSyn clinical criteria, >/=7% reduction in body weight has a beneficial impact on variables used to define MetSyn.