The average adolescent admitted to secure youth care is a 15-to 16-year-old boy who previously resided in an open youth care facility and who will stay for 6.5 months in secure youth care, before returning to an open youth care facility (Jeugdzorg Nederland, 2021). As mentioned earlier, adolescents admitted to secure youth care services represent a population with complex treatment needs. The majority suffers from multiple psychiatric diagnoses, a The reported AUCs concern a follow-up period longer than three months (mean follow-up was 3.13 years, SD = 0.66). * p < .05, ** p < .01, *** p < .001The START:AV authors emphasized the need for further research with the START:AV, including research with the final user guide, studies conducted by independent researchers, and field studies (i.e., using assessments conducted under real-world conditions; . This dissertation will address these issues and additionally introduce and examine the START:AV within a setting in which it has not previously been evaluated. The START:AV authors also indicated the need to assess implementation issues, such as how well the START:AV is applied according to the instructions in the user guide (i.e., fidelity). Without a proper implementation even the best risk assessment instrument will fail to produce desired This chapter is a slightly modified version of: