Mental illness typically onsets during the developmental stages from adolescence to emerging adulthood (ages 15–24 years), referred to as ‘youth’. A subset of youth with mental illness may be identified as having ‘complex’ mental health needs, defined based on requiring prolonged, extensive and resource-intensive services across multiple sectors, functional impairment, and comorbid challenges or multimorbidity . Effective early intervention for youth with complex mental illness is crucial to prevent the sequelae of long-term mental health problems. Several resource-intensive outpatient models have been developed to meet the needs of youth with complex mental illness; however, to the best of our knowledge, no scoping review has synthesised the available evidence on these interventions. A comprehensive synthesis of existing intensive outpatient interventions is needed to identify, target and inform future research and clinical efforts to better serve youth with complex mental illness. As such, the proposed scoping review will address the following research questions: (1) What intensive outpatient interventions have been evaluated for youth with complex mental illness? (2) To which populations are these interventions targeted? and (3) What outcomes have been examined within the context of these models?

This review will follow the Arksey and O’Malley framework for scoping reviews, and we will report the results following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) recommendations. We will conduct a comprehensive literature search across seven academic databases to identify relevant peer-reviewed material in English from 1990 to the present. Inclusion criteria will address evaluations of outpatient models of care with intensive components targeted to youth ages 15–24 with features of complex mental illness. Studies will be screened independently for eligibility by two reviewers in Covidence using clear inclusion criteria. We will then collate, summarise and present the findings to provide a comprehensive overview of the existing evidence.

Ethical approval will not be required, as no data will be collected for the proposed project. Results will be disseminated in peer-reviewed articles, presented at conferences and shared with stakeholders to inform the development, implementation and evaluation of comprehensive transdiagnostic services targeting youth with complex mental illness.