The proposed research is an empirical investigation of obesity/overweight in children and youth in the United States. A multivariate statistical model is specified in which obesity/overweight and diet choice are mutually determined. The data sets are the Ten State Nutrition Survey, 1968-1970 and the Health and Nutrition Examination Survey, 1971-75. The research emphasizes the identification of diet, activity levels, and parents' stature effects in the obesity/overweight outcome; family income, mother's education, and activity level effects in the choice of diet, and socioeconomic and obesity/overweight effects in the choice of activity level. The research should contribute significanly to the identification of the etiology of obesity/overweight in children and youth and help identify important public policy options.