Bullying almost always occurs in the presence of peers, most of whom do not intervene to stop it. This study examined the role of attachment, empathy, and gender in predicting the behavior of 105 middle school students who reported being either (a) defenders who actively intervened to stop bullying, or (b) outsiders who were either not involved or stood by passively. It was hypothesized that gender, attachment to mother, attachment to father, and empathy would predict whether children nominated themselves as defenders in bullying situations. A hierarchical logistic regression analysis indicated that these variables together significantly predicted whether children nominated themselves as defenders or outsiders. Gender was not a unique significant predictor. Attachment to mother contributed significant unique variance to the model, but attachment to father did not after accounting for gender and attachment to mother. Empathy contributed significant unique variance to the model even after accounting for all other variables. Results suggest that middle school personnel should openly discuss with students their roles in bullying interactions. In addition, teaching empathy towards others and involving parents may be critical components in comprehensive prevention programs. (Contains 3 tables.)