Youth in the legal system are vulnerable to initiation and escalation of opioid use. The transition period during which a young person is released from the institutional setting to the community is a critical window of opportunity for preventive intervention targeting the uptake and intensification of opioid and other drug use. Adaptive preventive interventions are a promising approach to systematically varying the timing and intensity of substance use preventive interventions for these youth. This pilot study of 30 youth (97% young men; 37% White; Mage = 18.34, SD = 1.84) examined the feasibility and acceptability of adaptive and nonadaptive preventive interventions that incorporate components of the Adolescent Community Reinforcement Approach with Assertive Continuing Care, Trauma Affect Regulation: Guide for Education and Treatment, and Motivational Interviewing using the Sequential Multiple Assignment Randomized Trial study design. Participants completed assessments at baseline, 1-month postrelease, and 2-months postrelease. Enrollment rate was 65%. Nearly three-quarters (73%) of enrolled youth had substance use disorder at intake. Moreover, 60% of enrolled participants completed the 2-month postrelease follow-up assessment. Participants reported high satisfaction with the interventionist interactions, and 95% indicated they would recommend the program to other youth. The pilot study revealed the need for several adaptations to study and intervention protocols. This pilot study provides evidence of the feasibility of a research-practice partnership with state juvenile rehabilitation facilities, successful recruitment of youth involved in the legal system, and feasibility and acceptability of adaptive preventive interventions spanning pre- and post-release for legal system-involved youth. (PsycInfo Database Record (c) 2024 APA, all rights reserved).