We examined the association of body mass index (BMI), body weight perception, and weight control behaviors with problematic Internet use in a nationwide sample of Korean adolescents. Cross-sectional data from the 2010 Korean Youth Risk Behavior Web-based Survey collected from 37,041 boys and 33,655 girls in middle-and high-schools (grades 7-12) were analyzed. Participants were classified into groups based on BMI (underweight, normal weight, overweight, and obese), body weight perception (underweight, normal weight, and overweight), and weight control behavior (no weight control behavior, appropriate weight control behavior, inappropriate weight control behavior). The risk of problematic Internet use was assessed with the Korean Internet Addiction Proneness Scale for Youth-Short Form. Both boys and girls with inappropriate weighty control behavior were more likely to have problematic Internet use. Underweight, overweight, and obese boys and girls were more likely to have problematic Internet use. For both boys and girls, subjective perception of underweight and overweight were positively associated with problematic Internet use. Given the negative effect of inappropriate weight control behavior, special attention needs to he given to adolescents' inappropriate weight control behavior, and an educational intervention for adolescents to control their weight in healthy ways is needed.