<p>The aims of this study are to develop and validate the Pretrial Risk Assessment and Psychosocial Needs Assessment Questionnaire (PRO-CESO, in Spanish) for Mexican adolescents being processed in the Criminal Justice System. The design of PRO-CESO took into account validated instruments, literature, and legal standards for item generation and adapted them accordingly. The validity study was performed through professional panels and cognitive interviews with adolescents at the Mexico City Juvenile Detention Center. Additionally, descriptive statistics, Gwet’s agreement coefficient (<i>AC2</i>), Lawshe’s Modified Content Validity Ratio (<i>CVR’</i>), and Content Validity Index (<i>CVI</i>) were calculated. For item generation, 19 of 27 potential instruments for pretrial risk and mental health needs assessment were analyzed. Overall, professionals agreed that PRO-CESO was a clear, coherent, relevant, and comprehensive tool (<i>CVI</i> = .80–.96). According to adolescent interviewees, most PRO-CESO items (56%) were adequate, but slight modifications were made to enhance comprehensibility and administration concerns. Results show that the PRO-CESO, grounded as it is on a doctrine of holistic protection, is a promising tool that could be used as a risk assessment and screening device to assist in the court’s decision regarding the best precautionary and protection measures to be implemented based on pretrial risk and psychosocial needs of the adolescents in question.</p>