Objectives: The purpose of this study was to investigate the effect of an 8-week aerobic exercise program on daily energy expenditure and intake in adolescents with normal-weight and with overweight or obesity. Methods: Prospective intervention study. The study included twenty-six adolescents aged between 14-18 years: 17 adolescents (8 girls and 9 boys) with normal-weight (BMI <85th percentiles for age and sex), and 9 adolescents (5 girls and 4 boys) with overweight or obesity (BMI 85th percentile for age and sex). The aerobic exercise program included 30 minutes of cycling performed on a Monark cycle ergometer 3 times a week for 8 weeks at an exercise target heart rate at 75% of participants’ heart rate reserve using the Karvonen formula. Total daily energy expenditure was measured with an indirect calorimeter wear for resting metabolic rate and a 7-day accelerometer for energy expenditure from physical activity. Energy intake was estimated with 24-hour recalls. Results: The aerobic exercise program did not have any significant effect on body weight. Significant effects of aerobic exercise on total daily energy expenditure (p=.051), energy expenditure from physical activity (p=.031) and total daily energy intake (p=.008) were observed, which mainly revealed a reduction in daily physical activity and energy intake following the exercise program. However, there was no significant effect of weight status and no interaction effect between of aerobic exercise and weight status for those three variables. Conclusions: Adolescents with normal weight, overweight or obesity not only reduced their daily total energy expenditure by reducing physical activity, but simultaneously decreased their total daily energy intake after an aerobic exercise program.