Background: Accidental injury represents the most common type of traumatic event to which a child or adolescent may be exposed, with a significant number of these children going on to experience posttraumatic stress disorder (PTSD). However, very little research has examined potential interventions for the treatment of PTSD in these children. The present trial aims to evaluate and compare child- and family-focused versions of a cognitive-behavioural early intervention for PTSD following accidental injury.Methods/Design: The principal clinical question under investigation is the efficacy of an early, trauma-focused cognitive-behavioural intervention for the treatment of PTSD in children following accidental injury. Specifically, we compare the efficacy of two active treatments (child-focused and family-focused CBT) and a waitlist control (no therapy) to determine which is associated with greater reductions in psychological and health-related outcome measures over time. The primary outcome will be a reduction in trauma symptoms on a diagnostic interview in the active treatments compared to the waitlist control and greater reductions in the family-compared to the child-focused condition. In doing so, this project will also trial a method of stepped screening and assessment to determine those children requiring early intervention for PTSD following accidental injury.Discussion: The present trial will be one of the first controlled trials to examine a trauma-focused CBT, early intervention for children experiencing PTSD following accidental injury (as opposed to other types of traumatic events) and the first within a stepped care approach. In addition, it will provide the first evidence comparing the efficacy of child and family-focused interventions for this target group. Given the significant number of children and adolescents exposed to accidental injury, the successful implementation of this protocol has considerable implications. If efficacious, this early intervention will assist in reducing symptoms of traumatic stress as well as preventing chronic disorder and disability in children experiencing acute PTSD following accidental injury.