BACKGROUND: Persistent behavioural difficulties are common following paediatric acquired brain injury (ABI). Parents and families also experience heightened stress, psychological symptoms and burden, and there is evidence of a reciprocal relationship between parent and child functioning, which may be mediated by the adoption of maladaptive parenting practices. Despite this, there is currently a paucity of research in family interventions in this population. The aim of this study was to determine the efficacy of Stepping Stones Triple P: Positive Parenting Program (SSTP), with an Acceptance and Commitment Therapy (ACT) workshop, in improving child outcomes and parenting practices following paediatric ABI. METHODS: Fifty-nine parents of children (mean age 7 years, SD 3 years, 1 month; 35 males, 24 females) with ABI (Traumatic injuries 58%, Tumour 17%, Encephalitis or meningitis 15%, Cardiovascular accident 7%, Hypoxia 3%) who were evidencing at least mild behaviour problems were randomly assigned to treatment or care-as-usual conditions over 10 weeks. Mixed-model repeated-measures linear regression analyses were conducted to compare conditions from pre- to postintervention on child behavioural and emotional functioning (Eyberg Child Behavior Inventory, Strengths and Difficulties Questionnaire) and dysfunctional parenting style (Parenting Scale). Assessment of maintenance of change was conducted at a 6-month follow-up. The trial was registered on Australian New Zealand Clinical Trials Registry (ID: ACTRN12610001051033). RESULTS: Significant time-by-condition interactions were identified on number and intensity of child behaviour problems, child emotional symptoms and parenting laxness and overreactivity, indicating significant improvements in the treatment condition, with medium-to-large effect sizes. Most improvements were maintained at 6 months. CONCLUSIONS: Group parenting interventions incorporating Triple P and ACT may be efficacious in improving child and parenting outcomes following paediatric ABI.