BACKGROUND Previous studies assessed the influence of parental weight status, sexual maturation, race-ethnicity, and energy expenditure among children, but few examined these issues comprehensively. OBJECTIVE The objective was to determine whether differences in energy expenditure among premenarcheal girls are related to the pubertal stage and the race-ethnicity of the girls or to the weight status of their parents. DESIGN We measured the body composition and the energy expenditure of 196 nonobese girls enrolled in a longitudinal study. Total body water was measured by the isotopic dilution of (18)O water. We measured resting metabolic rate with the use of indirect calorimetry and daily energy expenditure by the doubly labeled water method. We used established criteria to determine sexual maturation. Parental weight status was based on body mass index. RESULTS Resting metabolic rate was higher among girls with >or=1 overweight parent than among girls with 2 normal-weight parents. Total energy expenditure was also higher among girls with >or=1 overweight parent, but these results were of borderline significance. We found no effect of pubertal stage on resting metabolic rate. Nonresting energy expenditure was significantly lower among pubertal girls than among prepubertal girls. After adjustments for age and body composition, we noted that resting metabolic rate, nonresting energy expenditure, and total energy expenditure were all significantly lower among black girls than among white girls. CONCLUSIONS Differences in resting metabolic rate and total energy expenditure among premenarcheal girls were associated with parental weight status and the girls' race-ethnicity, whereas differences in nonresting energy expenditure were associated with pubertal stage and race-ethnicity. Whether the observed differences in energy expenditure persist after puberty and predict weight gain during puberty awaits the results of longitudinal analyses.