This study aims to build on existing knowledge about sibling childhood relationships and experiences in the field of disability to explore and understand the perspective of audlt siblings of people with autism and high support needs in the UK. Whilst the focus of the study is primarily on audlt siblings and their past and current experiences and needs for support, especially in relation to future planning, these perspectives will be contextualised by including the autistic sibling in the research where appropriate and a key professional nominated by the non-disabled sibling who is involved in providing or arranging support to their autistic brother or sister.