The study was conducted to assess the association or physical activity, television watching and energy intake with body fat in 514 adolescents(218 boys, 296 girls) aged 14-17 years. Comparison of the weight status evaluated according to some indicators based on weight and stature was made. The quantitative food frequency was used to determine intakes of total energy and energy from each macronutrient. Television-watching time was used as an index of inactivity and time spent performing extra-curricular physical exercise or playing was used a index of activity, BMI(body mass index) was used as index of body fat. Weight status varied by the indicators used. Using BMI, Broca and Rohrer index, 54-59% of boys and 38-57% of girls were underweight decreased(23% of boys and 26% of girls) and the of overweight increased (9.3% of boys and 7.8% girls), when adolescents whose BMI are<=15th percentiles for age and sex, and >= 85th percentiles of standard growth charts of Korean Children and aldosescents(1998) were classified as underweight and overweight, respectively, Girls tended to get fatter compared to boys who showed greater skeletal development. There were no significant correlations between BMI and total energy intake, energy intakes from macronutrient and physical activity level. These lack of association seems to be related to indication that BMI reflects total body mass rather than fatness. Mpreover, the effect of growth may interact with diet intake or physical activity level. Although BMI was not related to physical activity, television-watching time was negatively correlated with physical activity. Television-watching time was positiviely correlated with energy intake in girls. In adolescents, criteria for weigh status based on weight and stature must be age- and sex-specific in that weight status varied by indicators whether gender and higher were taken into consideration or not. If follows that each hourly increment of television watching may be related to fatness of adolescents, because hours certainly reduce the opportunity to be active and increase th energy intake.(Korean J Nutrition 34(1):39-47, 2001)