The process of transitioning young people from children’s or adolescents’ health services into adults’ services is a crucial time in the lives and health of young people and has been reported to be disjointed rather than a process of preparation in which they are involved. Such transitions not only fail to meet the needs of young people and families at this time of significant change, but they may also result in a deterioration in health, or disengagement with services, which can have deleterious long-term consequences. Despite the wealth of literature on this topic, there has yet to be a focus on what works for whom, in what circumstances, how and why, in relation to all young people transitioning from children’s into adults’ services, which this realist synthesis aims to address.

This realist synthesis will be undertaken in six stages: (1) the scope of the review will be defined; (2) initial programme theories (IPTs) developed; (3) evidence searched; (4) selection and appraisal; (5) data extraction and synthesis; and (6) finally, refine/confirm programme theory. A theory-driven, iterative approach using the ‘On Your Own Feet Ahead’ theoretical framework, will be combined with an evidence search including a review of national transition policy documents, supplemented by citation tracking, snowballing and stakeholder feedback to develop IPTs. Searches of EMBASE, EMCARE, Medline, CINAHL, Cochrane Library, Web of Science, Scopus, APA PsycINFO and AMED will be conducted from 2014 to present, supplemented with grey literature, free-text searching (title, abstract and keywords) and citation tracking. Data selection will be based on relevance and rigour and extracted and synthesised iteratively with the aim of identifying and exploring causal links between contexts, mechanisms and outcomes. Results will be reported according to the Realist And Meta-narrative Evidence Syntheses: Evolving Standards Quality and Publication Standards.

This realist synthesis forms part of the National Transition Evaluation Study, which has received ethical and regulatory approval (IRAS ID: 313576). Results will be disseminated through peer-review publication, conference presentations and working with healthcare organisations, stakeholder groups and charities.

NCT05867745.

CRD42023388985.