Introduction 
Emergent mental illness during adolescence affects daily functioning, causing disruption to daily activities, routines, and patterns. Multiple inter-related personal, social and environmental determinants influence the onset, nature and subsequent course of those difficulties. Research suggests a bi-directional relationship exists between mental health and activity choices. Activity-focused interventions such as occupational therapy may improve adolescent mental health related outcomes. In this study, we identify and select which activity-related determinants should be prioritised in the development of an occupation therapy-based intervention for adolescents with emerging mental health difficulties using expert consensus.