This study investigated personality correlates of early adolescents' tendency to either defend victims of bullying or to avoid involvement in bullying situations. Participants were 591 Dutch fifth- and sixth-grade students (X-bar[subscript age] = 11.42 years). Hierarchical regression models were run to predict these students' peer-reported defender and outsider behavior by their self-reported Big Five and Reinforcement Sensitivity scores. Agreeableness (i.e., politeness) positively predicted both behaviors. Emotional stability (i.e., impulse control) positively and extraversion (i.e., dominance) negatively predicted only outsider behavior. Finally, punishment sensitivity positively and reward sensitivity negatively predicted only outsider behavior. While agreeableness seems conducive to executing provictim interventions, lacking in dominance and a strong impulse control make actively avoiding involvement in bullying situations more likely. The latter also holds for early adolescents who are afraid of punishment and unresponsive to rewards. The findings suggest that antibullying interventions aiming at promoting defending in outsiders need to take the influence of personality into account.