Adolescence is a critical developmental stage when young people make behavioural and lifestyle choices that have the potential to impact on their health and wellbeing into adulthood. While risk-taking is important for healthy psychological development, for many, inappropriate risk-taking is significantly associated with health and social harm during adolescence and these harms persist well into adulthood. Young people involved in the criminal justice system are a particularly vulnerable group with a greater propensity to take risks that are likely to have long term impact on their future health and wellbeing. The RISKIT-CJS programme is a multi-component intervention encompassing both individual and group work and includes elements of motivational enhancement, psycho-education, psychosocial approaches, cognitive behavioural therapy and mindfulness. The study is a major multi-centre evaluation of RISKIT-CJS. The methodological approach is a mixed method, prospective, pragmatic randomized controlled trial with individual allocation, combining both quantitative and qualitative evidence. The study will be conducted across three geographical areas; South East England, South London, North East England, covering a diverse socio-economic and ethnic population. Start date: 01/09/2016 End date: 31/08/2019 Funder: NIHR Public Health Research Funding £892,675