We examined client outcomes from the implementation of Multisystemic Therapy (MST) in a statewide child and adolescent mental health system. Specifically, we examined (1) the validity of therapist-rated MST outcome measures by comparing them to ratings of functional impairment and level of service needs by CAMHD care coordinators, who provide case management and care coordination services, (2) potential client and service predictors of therapist-rated outcomes, and (3) improvement in youth functioning around the time of entry to and exit from MST compared with rates of improvement reported in randomized controlled trials (RCTs) by the developers of MST. Results suggested that therapist-rated MST outcomes were valid indicators of treatment success. Similar to other findings in the MST literature, few client or service characteristics predicted these outcomes. Finally, although MST entry–exit effect sizes were lower than the mean derived from RCTs published by the developers, they were within the 95% confidence interval. Together, these findings support the implementation of MST in complex systems of care with continued attention to quality assurance and ongoing use of data for evaluation.