["Health Expectations, Volume 29, Issue 3, June 2026. ", "\nABSTRACT\n\nBackground\nTrans and gender diverse (trans) young people experience higher rates of physical and mental ill‐health due to chronic exposure to gender minority stress. Consequently, trans young people report higher health and mental healthcare service utilisation. Disconcertingly, negative experiences of healthcare services are prevalent among trans young people, especially those with additional marginalised identities and backgrounds who experience multiple forms of marginalisation. Patient‐reported experience measures (PREM) are auseful tool for improving patients' healthcare experiences however existing PREMs are not relevant, appropriate, nor inclusive of the unique healthcare experiences of trans young people, especially those facing additional forms of marginalisation.\n\n\nObjective\nThis study will co‐develop and validate a PREM for trans young people aged 12 to 25 years attending health and mental healthcare services. This PREM will capture how healthcare experiences should affirm all aspects of trans young people's identities in health and mental health services, including but not limited to their gender.\n\n\nDesign\nUnderpinned by a ‘co‐production’ framework, the proposed study comprises four stages informed by a Lived Experience Advisory Group (LEAG) made up of eight trans young people from across Australia. Stage 1 is a scoping review of qualitative studies exploring the experiences of marginalised young people using healthcare services. Stage 2 is semi‐structured, one‐to‐one interviews with multiply marginalised trans young people aged 12 to 25 years in Australia (n = 30) and healthcare professionals of trans young people in Australia (n = 30). Candidate PREM items generated from Stages 1–2 will be appraised in a multi‐stakeholder modified e‐Delphi Consensus Survey (N = 90; Stage 3) comprising multiply marginalised trans young people (n = 30), healthcare professionals (n = 30), and parents/caregivers of trans young people (n = 30). Lastly, in Stage 4, PREM items will be reviewed by trans young people in two cognitive debriefing focus groups (N = 14) to improve clarity, understandability, and interpretation.\n\n\nDiscussion\nThis study will co‐produce and validate a PREM to effectively measure the quality of trans young peoples' experiences utilising health and mental healthcare services. The PREM will subsequently be implemented into integrated youth health services as part of a multi‐staged quality improvement project evaluating an integrated gender service model of care operating in Victoria, Australia.\n\n\nPatient or Public Contribution\nThe Whole of Self Affirming Care Lived Experience Advisory Group together with trans members of the research team in designated peer and non‐peer research roles have contributed to the design of the present study protocol and corresponding manuscript. These individuals will also contribute to analysis, interpretation, and write‐up of all subsequent data and outputs.\n"]