Arrest rates among the population of youth who have been served in child mental health systems are known to be high during adolescence and young adulthood, but individual longitudinal patterns have not been examined. The present study used developmental trajectory modeling, a contemporary method used widely in criminology, to examine clusters of individual criminal justice involvement patterns at ages 8 through 25, from database records of 131 individuals in public adolescent mental health services. Three groups of particular concern emerged: one with increasingly high offense rates and two with moderate to high violent offense rates that did not desist. Offense patterns in these groups indicate that early intervention should occur before age 15. Some risk factors were identified. Peak offending for most groups occurred between ages 18 and 20. Implications of these findings for mental health services during the transition to adulthood are offered.