The main aim of this study is to assess whether lack of self-control or the perceived costs and benefits of aggression provide the better predictors of bullying behavior and victimization, and direct aggression perpetration, in a sample of 122 male British prisoners. We also assessed whether bullying was associated with height and weight. Zero-order correlations showed that perceived benefits, self-control, and perceived costs were most closely associated with perpetration of bullying, and that lack of self-control was weakly associated with victimization. Height and weight were unrelated to bullying or victimization. In a standard regression analyses, perceived benefits was the strongest predictor of bullying perpetration, with lack of self-control contributing further; all three variables made a significant contribution when direct aggression was the criterion. Mediation analysis showed that a combined cost-benefit measure partially mediated the association between self-control and both bullying and direct aggression. The findings are discussed in relation to explanations of aggression based on impulse control or a cost-benefit analysis.