The use of structured risk assessment instruments is recommended for service agencies that detain and/or treat youth with mental health and behavioral problems who pose a risk to themselves or others. The Short-Term Assessment of Risk and Treatability: Adolescent Version (START:AV) is an example of a risk assessment instrument for adolescents. It is used to assess the risk of multiple adverse outcomes, including violent offending, victimization, and substance abuse. In this dissertation, the implementation and field psychometric properties of this instrument were evaluated in a Dutch secure youth care facility. First, the implementation process was examined closely. Which factors are hindering or facilitating the process? How successful is the implementation according to various implementation outcome indicators? Second, the interrater reliability and predictive validity of the START:AV were examined. The findings of this dissertation provide insight into the practical utility of the START:AV in this specific population under real-life circumstances.