Currently, implementation research in the field of forensic risk assessment is limited and consensus on “implementation success” is lacking. This study applies outcomes of success from implementation science to the implementation evaluation of the Short-Term Assessment of Risk and Treatability: Adolescent Version (START:AV) in a residential youth care facility in the Netherlands. Staff perceptions on the implementation and the instrument were assessed using 5 implementation outcomes in a longitudinal multimethod design: acceptability, adoption, appropriateness, feasibility, and penetration. As anticipated, the majority of staff perceived START:AV core constructs as useful for treatment (appropriateness). However, satisfaction with the instrument decreased over time (acceptability). This was likely due to an increased workload (feasibility). Despite this dissatisfaction, the completion rate was acceptable (adoption). Lastly, staff reported a lack of integration of the START:AV findings in clinical case conferences (penetration). The implementation outcomes aid in identifying areas for improvement, which in turn can lead to an increased and more consistent uptake of structured risk assessment into routine practice