This study reports a short-term prospective investigation of the role of peer group victimization in the development of children's behavior problems, at home and in school. Sociometric interviews were utilized to assess aggression, victimization by peers, and peer rejection, for 330 children who were in either the third or fourth grade (approximate mean ages of 8-9 years old). Behavior problems were assessed using standardized behavior checklists completed by mothers and teachers. A follow-up assessment of behavior problems was completed 2 years later, when the children were in either the fifth or sixth grade (approximate mean ages of 10-11 years old). Victimization was both concurrently and prospectively associated with externalizing, attention dysregulation, and immature/dependent behavior. Victimization also predicted increases in these difficulties over time, and incremented the prediction in later behavior problems associated with peer rejection and aggression. The results of this investigation demonstrate that victimization in the peer group is an important predictor of later behavioral maladjustment.