To determine the accuracy of self-reported weights and heights and of relative weight status in a sample of American Indian adolescents, a survey was conducted in middle and high schools on or near three Indian reservations-Navajo, Choctaw, and Blackfeet. Self-reported weights and heights were compared with measured weights and heights. Participants were 12 through 19 years old. (N = 806, 47.4% male). Overall, both boys and girls underreported weight (mean difference = self-reported - measured mean values)(-3.4 +/- 13.1 and -4.6 +/- 13.0 lb, respectively) and overreported height (0.6 +/- 2.1 and 0.2 +/- 2.6 in, respectively) However, underweight boys and girls overreported weight (normal: -1.6 +/- 7.9 and -1.4 +/- 6.3; overweight: -7.5 +/- 17.9 and -11.6 +/- 19.0 lb, respectively). Although correlations between measured and reported weight, height, and body mass index (BMI) were high, the sensitivity of relative weight categories based on BMI using self-reported weight and height compared with measured weight and height was poor: 66.7% for underweight (BMI < 15th percentile, based on a national reference population), 88.9% for normal weight, and 73.6% for overweight (> 85th percentile). These results call into question the accuracy of self-reported weight and height measurements among American Indian youth and are similar to findings among non-American Indian adolescents. Therefore, their use in prevalence studies should be avoided, and they should be used cautiously in other types of epidemiologic studies.