In this paper empirical evidence is presented on the determinants of obesity in youth in the U.S., with particular emphasis on isolating the effects of diet and parent's fatness on the obesity outcome. The results show that parents fatness has statistically important impacts on skinfold growth among children and adolescents. Diets between obese and non-obese youth, however, do not differ substantially. Evidence that youth with "fatter parents" are able to produce more skin-fold or adipose tissue from given calorie intakes includes the significant and relatively large parent's fatness (skinfold) effects in the youth skin-fold equations, the larger calorie coefficients in the skin-fold equation for 10-16 year old youths with "fat" mothers as compared to 10-16 year olds with around average mothers, and the significant and relatively large parent's fatness effects in the youth obesity probability equations. The probability models show that if either of the parents of a 10-16 year old is obese, the probability of the 10-16 year old being obese is .2, holding constant age, race, sex and calorie consuiption. If both parents are obese the probability of the 10-16 year old being obese is .4.The data set is the Ten State Nutrition Survey,1968-1970.