To determine if self-reported negative social interaction mediates the relationship between sedentary behavior and body mass index (BMI) percentile in boys. Twelve overweight/obese (?85th BMI percentile) and 14 non-overweight (<85th BMI percentile) boys (10.5 ± 1.5 years old) completed surveys assessing overt peer victimization and relational victimization. Children were individually given access to a gymnasium with physical activity equipment and sedentary alternatives for 30 minutes. Children could play with the equipment in any pattern they wished and the amount of time allocated to sedentary activities (sitting time) was recorded. Overt and relational victimization were moderately and positively associated with BMI percentile (r ? 0.40, p ? 0.04) and sitting time (r ? 0.40, p ? 0.05) and sitting time was positively associated with BMI percentile (r = 0.4, p = 0.05). After controlling for overt and relational victimization the correlation between sitting time and BMI percentile was non-significant (r ? 0.28, p ? 0.18). The positive relationship between BMI percentile and sedentary behavior was mediated by measures of negative social interaction.