Little is known about high-cost service users in the context of youth outpatient mental health, despite the fact that they account for a large proportion of overall mental healthcare expenditures. A nuanced understanding of these users is critical to develop and implement tailored services, as well as to inform relevant policies. This study aims to characterize high-cost service users by examining demographic factors, diagnoses, and service type use. Administrative service use data were extracted from a large County Department of Behavioral Health Services database. Latent profile analyses suggest a fourprofile solution primarily distinguished by youth age and diagnostic complexity. Study findings have implications for defining high-cost service users and key targets for efforts aiming to improve outcomes for these youth.Keywords Public mental health services • Youth • High-cost users • Pattern-oriented approach Mental health conditions are the fifth leading cause of nonfatal disease worldwide (Whiteford et al. 2013). As many as 20% of youth experience one or more mental health conditions (Kessler et al. 2005), resulting in poor functional, vocational, educational, and health outcomes, including further mental health and medical issues (Jaycox et al. 2009). Youth mental health conditions have a deleterious public health impact through the large cost to individuals, families, communities, and health care systems (U.S. Department of Health and Human Services 2001). The cost-saving benefits of children receiving appropriate, effective, and evidencebased care in community-based mental health settings