Background: Diagnosis of life threatening childhood illness or injury can lead to significant distress reactions in parents, with many experiencing clinically significant levels of post-traumatic stress symptoms. These symptoms can have long-term adverse impacts on parent mental health, family functioning, and the adjustment of the ill child. Independent studies have found such reactions in several different illness groups. However, very little research has systematically compared the prevalence, impact and trajectories over time of post-traumatic stress symptoms in parents across different childhood illness groups with an acute life threat. The current study seeks to map the course of post-traumatic stress reactions in parents of children with various life threatening illnesses over an 18 month period, and identify factors that predict successful adaptation in families. Method/Design: The current study described is of a prospective, longitudinal design. The sample included parents of children admitted to four major hospital departments at the Royal Children’s Hospital, Melbourne, Australia, for a life threatening illness or injury. Eligible parents were those who were caregivers of children aged 0-to 18-years admitted to the Oncology, Cardiology, Neurology and Pediatric Intensive Care Unit. Parents were recruited acutely, and completed self-report questionnaires at four time-points: within the first 4 weeks (T1:); then at 4 months (T2); 7 months (T3); and 19 months (T4) after admission. Questionnaires assessed parent and child mental health and wellbeing, and a number of risk and reliance factors such child illness factors, parent demographic factors, and psychosocial factors. Discussion: This study is one of the first to document the trajectory of post-traumatic stress responses in parents of very ill children, across illness groups. Given that it will also identify risk and resilience factors, and map the course of parent outcomes over an 18 monthperiod, it has the potential to inform novel strategies for intervention.