Bullying studies frequently rely on student self-report to identify bullies and victims of bullying, but research in the broader field of peer aggression makes greater use of other informants, especially peers, to identify aggressors and victims. This study compared self, peer, and teacher identification of bullies and bully victims in a sample of 416 middle school students. Overall, there was poor correspondence between self-reports and reports made by peers or teachers, but consistently better agreement between peers and teachers, in identifying both bullies and victims of bullying. Peer and teacher identification of bullies were more consistently associated with subsequent school disciplinary infractions than were self-reports. These results raise concern about reliance on student self-reports of bullying and bully victimization. (Contains 1 note and 8 tables.)