This dissertation consists of a series of papers which focused on creating age-, sex-, and ethnicity-specific body fat centiles and the concordance of those centiles with other commonly used childhood obesity indices. Anthropometric and body composition data of 5 to 18 year olds were taken from a large, multi-ethnic, nationally-representative sample participating in one of three cycles of the National Health and Nutrition Examination Surveys. Percent body fat (%BF) was calculated using tricep and subscapular skinfold measurements within the commonly used Slaughter equations. %BF growth curves were created for white, black, and Mexican-American children and adolescents. Values were provided so that future researchers can identify children based on these reference data. In addition, the concordance of single-value body fat cutpoints, Body Mass Index (BMI) centiles, Waist Circumference (WC) centiles and %BF centiles was examined. It was found that BMI and WC centiles demonstrated a reasonable level of agreement with the single-value %BF cutpoints of 25% and 30% in boys and girls, respectively. However, current Centers for Disease Control BMI cutpoints for obesity have low sensitivity and high specificity when compared to these values. Further, BMI and WC centiles agreed more consistently with single-value %BF cutpoints in boys than girls. Using receiver operator characteristic (ROC) curves, it was indicated that %BF centiles corresponded consistently with currently used BMI cutpoints for overweight and obesity. Furthermore, the values of sensitivity, specificity, and area under the ROC indicated no large discrepancies between the sexes or among ethnic groups. The optimal %BF values identified at younger ages were well below the single-value %BF cutoffs of 25% and 30% fat. The LMS-derived %BF centiles can be used to improve agreement between %BF measures and current BMI classification systems. Single-value, or static, %BF thresholds are not sensitive to growth and maturation and should not be used across the pediatric age range.