Purpose: This study examined agreement between all 3 standards (as well as relative diagnostic associations with metabolic syndrome) using a representative sample of youth from the Hungarian National Youth Fitness Study. Method: Body mass index (BMI) was assessed in a field sample of 2,352 adolescents (ages 10-18.5 years) and metabolic syndrome status was assessed in a laboratory subsample of 373 youth. All youth were categorized into weight status groups based on the FITNESSGRAM®, International Obesity Task Force (IOTF), and Hungarian growth standards. Classification agreement was compared between all pairs of standards via cross-tabulation. Logistic regression was used to estimate the odds of metabolic syndrome by weight status. Results: The 3 BMI standards agreed on =88% of cases, with better agreement on girls' standards than boys' standards. Kappa values ranged from 0.65 to 0.89. Using the Hungarian standards over the Fitnessgram or IOTF standards resulted in 5% to 10% more youth being classified as normal weight. The overweight/obesity groups were 4 times to 6 times more likely to have metabolic syndrome than those classified as normal weight regardless of the classification standards. These odds ratios increased to 8 times to 17 times when comparing the normal-weight/overweight groups to the obesity category. Odds ratios for boys tended to be slightly larger than those for girls. Conclusions: All 3 standards provide similar information about weight status and metabolic syndrome classification. To more easily facilitate international comparisons, it may be of greater benefit to use the IOTF standards, which also had better agreement with the U.S. Fitnessgram thresholds.