To investigate the prevalence of posttraumatic stress symptoms in parents of children who have been supported on extracorporeal membrane oxygenation and to explore associated factors. Descriptive cross-sectional study. A specialist pediatric tertiary center in the United Kingdom. Parents (n = 52) of children who had been supported with extracorporeal membrane oxygenation at least 6 months previously. None. Self-reported questionnaires were completed measuring posttraumatic stress symptom, family functioning, depression, anxiety, and demographic variables. Approximately 20% of parents experienced posttraumatic stress symptoms at levels suggestive of a diagnosis of posttraumatic stress disorder, irrespective of the time that had elapsed since extracorporeal membrane oxygenation. Although having a child who had ongoing illness before extracorporeal membrane oxygenation was associated with avoidance posttraumatic stress symptoms, results suggest that other previously identified risk factors, such as gender and family functioning, may not be risk factors for posttraumatic stress symptom in this population. A substantial number of parents in this population experience posttraumatic stress symptom. Psychological interventions may be targeted toward those whose child has had ongoing illness before extracorporeal membrane oxygenation.