This study aims to evaluate the effectiveness of the Multisystemic Therapy (MST) intervention for Australian families invloved with the Specialist Child and Adolescent Mental Health Service (CAMHS). This program was implemented within the Western Australian Department of Health in 2005, and has continually operated two small clinical teams within the Perth metropolitan area since then. This intervention was specifically chosen to improve service access, engagement, and intervention with vulnerable families having young persons with a history of significant and enduring behavioural problems. The study reports on data collected from July 2007 to July 2013 which includes baseline, post‐treatment, 6‐month, and 12‐month follow‐up. There were 153 MST families participating in the research at all time points (71% male; 11% Australian Aboriginal; average youth age was 13.6 years). Caregivers completed a set of questionnaires including Child Behaviour Checklist, Parenting Styles and Dimensions Questionnaire, and Depression, Anxiety and Stress Scale. One‐way repeated measure ANOVA were used to measure changes over time. Significant caregiver‐reported improvements in all measures were reported at post‐treatment, and most improvements were maintained at the follow‐up periods of 6 and 12 months post‐intervention. These preliminary outcomes demonstrate that the 4–5 month MST intervention significantly reduces behavioural problems and emotional difficulties in young Australians and these improvements are generally maintained by caregivers over time. Primary caregivers reported improved skills and mental health functioning that were also maintained over the follow‐up period. A proposed randomised controlled trial of the program will address potential placebo and selection bias effects.