Stature, weight, and body mass index (BMI) were obtained by self-reports and by measurements for 69 American Indian youth, 12-19 years of age, to determine the validity of self-reported values for research and clinical use. Self-reported weight was significantly less than measured weight by 2.64 kg and 2.76 kg for boys and girls, respectively. There was no systematic bias in self-reported stature in either sex. BMI based on self-reported values was significantly less than measured BMI by about 1 kg/m2 in each sex. Reporting errors for weight and BMI were related to measured size, with the greatest under-estimates at the highest values of measured weight and BMI. If the patterns observed in this sample exist more widely, self-reported measures may not be acceptable proxies for measured values.