ABSTRACT. Objective. To determine the period of childhood in which weight relative to height increases in Pima Indian children and young adults in comparison with the general US population.Methods. Heights and weights of children in the Pima Indian population were derived from either clinical examinations conducted by the Department of Public Health Nursing (from 1-48 months of age), or from examinations in the National Institutes of Health longitudinal survey of health in the Pima population (for birth and ages 5-20 years), and compared with standards for the US population recently published by the National Center for Health Statistics.Results. Weight relative to height (weight-for-length in children aged <24 months, body mass index at ages >2 years) was significantly higher in Pima children at all ages examined after the first month of life. Compared with reference values, the most dramatic increases in weight relative to height occurred in 2 stages of childhood: mean z scores of weight-for-length increased between 1 month (mean ؎ SEM: males: ؊0.2 ؎ 0.19; females: ؊0.02 ؎ 0.14) and 6 months (males: 0.8 ؎ 0.04; females: 0.7 ؎ 0.04) of age; mean z scores for body mass index increased gradually between 2 years (males: 0.4 ؎ 0.06; females: 0.4 ؎ 0.08) and 11 years (males: 1.4 ؎ 0.08; females: 1.4 ؎ 0.08) and remained stable thereafter.Conclusion. Excessive weight gain occurs early in the Pima population with changes relative to reference values most marked in the first 6 months of life and between 2 and 11 years. Interventions toward primary prevention of obesity may need to be targeted at children rather than adults in this population. Pediatrics 2002; 109(2). URL: http://www.pediatrics.org/cgi/content/full/ 109/2/e33; Pima, Native American, body mass index, obesity.ABBREVIATIONS. BMI, body mass index; NIH, National Institutes of Health; SD, standard deviation; CDC, Centers for Disease Control and Prevention; NCHS, National Center for Health Statistics; NHANES, National Health and Nutrition Examination Survey.T he prevalence of obesity continues to rise in the United States, prompting interventions on the individual and population level to try to prevent and treat the condition. 1,2 The Pima Indians of Arizona have a particularly high prevalence of obesity in both adults and children and suffer from a variety of secondary health consequences-most notably high rates of type 2 diabetes. 3 Excess weight gain in childhood is important for a number of reasons. First, obesity is increasingly recognized in pediatric populations, with attendant concerns regarding immediate and future effects on health. 4 In the Pima population, both obesity and type 2 diabetes are recognized as important health problems in childhood. 5,6 Second, weight gain in childhood may be an important antecedent of obesity in adult life. Body mass index (BMI) tracks through childhood, so that childhood BMI predicts adult obesity. 7 The disappointing results of attempts to treat obesity in adults and children have led to suggestions that health care ...