NIHR funded a 5 year Programme Grant for Applied Research to explore how to promote the subjective wellbeing and health of young people with long term conditions by generating evidence to enable NHS Commissioners and Trusts to facilitate the successful transition of young people from child to adult health care, thereby improving health and social outcomes. It completed in September 2017. I shall cover some background to transition, then summarise the purpose of the Programme and the methods of it work packages. I shall then report the main results and implications of the Research programme. One of the work packages was a longitudinal study. We had annual contact over 4 years with a cohort of 374 young people, aged over 14 and pre-transfer on entry to the study. Each had one of three conditions: Diabetes mellitus as an exemplar of a chronic illness; Cerebral palsy as an exemplar of a complex physical impairment; Autism and associated mental health problem as an exemplar of a complex mental health and neurodevelopmental problem. I shall draw out similarities and differences between these three groups with respect to the outcomes and process measures that we captured.