This study examined the relation of elementary-school children's externalizing behaviour to emotion attributions, evaluation of consequences, and moral reasoning. Externalizing behaviour was rated by the parents using the Child Behaviour Checklist (CBCL/4 - 18). Moral development was assessed by three stories describing different types of rule violation and a moral conflict in friendship including obligations and self-interest. The children were asked about the emotions they would attribute to the hypothetical victimizer (or protagonist) and the self-as-victimizer (or protagonist), the evaluation of the interpersonal consequences of the rule violation (or action decision) as well as their justifications. Boys who made selfish action decisions and attributed positive emotions to the protagonist of the moral dilemma displayed more externalizing behaviour than girls. Furthermore, boys with consistent moral (negative) emotion attributions to the self-as-victimizer across the rule violations showed less externalizing behaviour than boys with inconsistent moral emotion attributions. Younger children who anticipated negative interpersonal consequences of transgressions displayed higher rates of externalizing behaviour than younger children who anticipated less negative consequences. Moral reasons in the context of emotion attributions to the self-as-victimizer were negatively associated with externalizing behaviour.