‘Social exclusion’ describes the process whereby certain groups are excluded from mainstream society. For example, people who have experienced homelessness, prison or engaged in sex work are often cited as exemplars. Recent evidence indicates that these groups experience extreme health inequalities, including adverse mental and physical health, elevated mortality and barriers to accessing services. Yet an understanding of how mental and physical health interact in those who are socially excluded remains poorly understood. Commentators have also called for further conceptual clarity on the nature of ‘social exclusion’ and intersectional factors (such as material deprivation, childhood trauma and social/ economic marginalisation) over the life-course which may lead to social exclusion. This mixed methods study will provide systematic assessments of physical and mental health inequalities in the above groups, enriched by the perspectives of people with lived experience of social exclusion. The CASE partner for this project, Rethink Mental Illness, are a charity known for their commitment to tackling social exclusion in people with mental illness. With their support, the student will be able to access people who have first-hand experience of social exclusion which will inform the qualitative part of the study, as well as access to service user involvement groups, enhancing co-production of the research. Rethink will provide unique opportunities for dissemination. The outputs will inform Rethink’s work with the NHS on the coproduction of community services for these groups. The project aims are to: • Assess the prevalence of mental and physical health problems for socially excluded groups, and associations with mortality. • Understand how mental/physical health comorbidities and service use interact with social exclusion The quantitative part of the study will use information from the Adult Psychiatric Morbidity Surveys (APMS) from 2007 and 2014, as well as the Clinical Record Interactive Search (CRIS) case register. The APMS is a nationally representative survey with information on mental and physical health, as well as experiences of social exclusion (e.g. homelessness). CRIS is a case register of de-identified Electronic Health Records of patients using secondary mental health services in south London and will provide a clinical cohort with information on service use and deaths. Qualitative interviews will be conducted with people with lived experience of social exclusion to investigate barriers and facilitators when accessing healthcare. The outputs from this research will provide a holistic picture of the interplay between social exclusion and health.