Research indicates moderate-to-limited integration of the risk-need-responsivity (RNR) principles in probation case planning. Efforts to improve implementation are important targets for research, policy, and practice. This study examined the ability of two juvenile probation departments to implement RNR principles with fidelity following a comprehensive implementation protocol that included RNR-related policies, creation of a service matrix for criminogenic need-to-service matching, and extensive staff training.The researchers anticipated fidelity to the risk and need principles would be stronger than previous studies.This implementation study involved secondary data analysis of services received over 10 months for 254 adolescent offenders (76.80% male, 72.40% White, M age = 16.13 years) from two probation departments following adoption of the Youth Level of Service/Case Management Inventory.Probation departments evidenced strong fidelity to the risk principle, such that higher risk youth were assigned more services with higher intensity. Fidelity to the need principle was moderate at best (an average 24.61% to 29.38% need-to-service match) and varied by criminogenic need, overall risk level, and the operational definition of criminogenic need.Comprehensive implementation practices are associated with strong fidelity to the risk principle, but it may take longer for probation departments to achieve strong fidelity to the need principle. Researchers should identify more feasible methods for implementing the need principle and strive for a consensus on methods for measuring need-to-service match that are also consistent with probation policies. (PsycINFO Database Record (c) 2019 APA, all rights reserved).