Addressing the specific needs of youth across multiple life domains as they transition from the children’s behavioral health treatment system to the adult treatment system is critically important. To help quantify these issues and contribute to discussions related to system interventions locally, Allegheny Health Choices, Inc. (AHCI) identified a cohort of youth who turned 17 between January 2007 and December 2009 and used behavioral health services while 17. This report describes their service use characteristics and involvement with other systems during their 17th year compared to their 18th year.