Finding show that juvenile sex offenders whose victims were children tended to target male and female relatives, and juvenile sex offenders whose victims were peers tended to target girls unrelated to them. Peer offenders had a more extensive criminal history than child offenders, which is consistent with previous research that shows this group generally engages in more disruptive behavior than child offenders. Although the mixed offender subgroup accounted for only 7 percent of the total sample of juvenile sex offenders, the findings show they differed from the child and peer offenders in several important ways. They exhibited more diverse and physically intrusive sexual offense histories than the other subgroups and were less likely to complete treatment. The findings show the importance of including mixed offenders in future research, in order to examine the varying etiology of sexual offending, treatment, and reoffending among juvenile sex offenders. All of the study participants had been committed to a North Florida residential training school between 1995 and 2001. Commitment to this facility was limited to serious and/or chronic sexual and nonsexual offenders between the ages of 12 and 19. The majority were required by the court to complete a 12-month sex offender treatment program. Data were obtained on their sex offenses, nonsexual offenses, progress in treatment, and reoffending for nonsexual and sexual offenses following release from the facility. 2 tables and 33 references