['This study examines the relationship between physical activity (PA), sedentary behavior (SB) and body weight in Korean adolescents.', 'This study used a nationally representative sample of 72,368 South Korean adolescents, aged 13 to 18 years. The study sample was categorized according to BMI as follows: underweight, body mass index (BMI) <18.5; normal weight, 18.5 ≤ BMI < 23.0; overweight, 23.0 ≤ BMI < 25.0; and obese, 25.0 ≤ BMI. An analysis was then performed to determine if meeting the recommended guidelines for PA frequency (5 times/week ≤) and amount of SB (<2 hours/day) was associated with weight category.', 'The percentage of normal weight adolescents was 54.3% while the percentages of underweight, overweight, and obese adolescents were 27.4%, 10.2%, and 8.1%, respectively. Significantly fewer underweight and obese adolescents met PA guidelines compared to normal weight adolescents. In addition, underweight, overweight, and obese adolescents had significantly higher SB scores.'] Do physical Activity and Sedentary Behavior Are Independently Associated with Weight in Korean Adolescents?