Current best practice therapeutic intervention for traumatised children is based on the trauma paradigm. However, there is little published research that examines the efficacy of the Play Therapy Dimensions Model (PTDM) with this population. Therefore, this study was designed to explore the utility and neurobiological mechanisms of the PTDM in play therapy with traumatised children. The methodology employed was a retrospective analysis using mixed-methods in a systematic, single case study design, with the study occurring over a 10-week period. The case for study was an individual therapeutic process of a 7½ year old male. Methods used were review of the child’s case file and the researcher’s play therapy process diary, and data from the following psychometric measures and therapist reflection form: Behaviour Assessment System for Children – Second Edition (Parent Rating Scale), Trauma Symptom Checklist for Young Children, and the PTDM Child and Therapist Moderating Factors form. Results clearly demonstrated the efficacy of the PTDM in play therapy with traumatised children, resulting in clinically significant improvements in the child’s trauma symptomology. Moreover, the trauma paradigm identified specific neurobiological mechanisms central to this process leading to the development of a new clinical practice model, the Play Therapy Dimensions Model – Revised (PTDM-R). Finally, the research demonstrates how with the inclusion of a new neurobiological domain – Regulation and Window of Tolerance – that the PTDM-R is applicable to all play therapy modalities regardless of theoretical orientation.