OBJECTIVES: The study objectives were to develop age-specific adolescent metabolic syndrome (MetS) criteria that were linked to the health-based Adult Treatment Panel III (ATP) and International Diabetes Federation (IDF) adult criteria. BACKGROUND: There has been no consistency in the criteria used to diagnose the MetS in adolescents. Studies have either applied adult criteria or arbitrarily chosen adolescent high-risk cut-points. METHODS: The adolescent (12 to 19 years old) MetS criteria developed in this study were linked to the ATP and IDF adult criteria with LMS growth curve modeling for each MetS component (waist circumference, systolic and diastolic blood pressure, high-density lipoprotein cholesterol, triglycerides, and glucose). Nationally representative data from the National Health and Nutrition Examination Surveys were used to develop the growth curves. RESULTS: The growth curves for each MetS component passed through the ATP and IDF cut-points at 20 years of age such that adolescent cut-points were linked to the adult values. Age- and gender-specific cut-points for each MetS component were developed that can be used to define high-risk values in 12- to 19-year-olds. The prevalence of MetS in adolescents nearly doubled over the last decade and was 7.6% on the basis of the newly developed ATP adolescent criteria and 9.6% on the basis of the newly developed IDF adolescent criteria. CONCLUSIONS: These new criteria should provide improved and age-appropriate approaches for diagnosing MetS among adolescents.