BACKGROUND Waist circumference (WC) may be a better predictor of cardiovascular disease risk than body mass index (BMI). We provide the most current WC percentile estimates for the U.S. Mexican-American (MA), non-Hispanic black (NHB), and non-Hispanic white (NHW) pediatric populations. METHODS Percentile regression analyses were used to estimate the 10(th), 25(th), 50(th), 75(th), and 90(th) percentiles of the distribution of WC for boys (n=8,351) and girls (n=8,054) for ages 2-18 by ethnicity using the combined 1999-2008 National Health and Nutrition Examination Surveys. RESULTS MA boys were over 2.5 times as likely versus NHB [odds ratio (OR)=2.60, 95% confidence interval (CI) 1.73-2.52] and almost twice as likely versus NHW (OR=1.86, 95% CI 1.73-2.52) to have a WC above the 90(th) percentile. NHB (89.1 cm) and MA (88.8 cm) girls ages 11 and older and NHW girls (88.7 cm) ages 12 and older who had a WC at or above the 90(th) percentile meet adult WC criteria for the metabolic syndrome (88 cm). MA boys (105.1 cm) ages 14 and older, and NHB (105.1 cm) and NHW boys (105.0 cm) ages 16 and older that had a WC at or above the 90(th) percentile meet adult WC criteria for the metabolic syndrome (102 cm). CONCLUSIONS WC is a simple, inexpensive measure that can identify children at risk for cardiometabolic disease. A large proportion of U.S. adolescents with elevated WC, and prepubescent girls in particular, currently meet adult cutoff criteria for WC as a component of the metabolic syndrome.