OBJECTIVE: We aimed at evaluating surgery-related posttraumatic stress disorder (PTSD) in parents of children undergoing cardiopulmonary bypass surgery. Risk factors for parental PTSD symptoms were explored. DESIGN: A prospective cohort study was performed assessing PTSD symptoms immediately after discharge and 6 months after cardiopulmonary bypass surgery. SETTING: Recruitment took place at a tertiary pediatric medical center in Switzerland. SUBJECTS: German-speaking parents of children with congenital heart defects aged between 0 and 16 yrs undergoing cardiopulmonary bypass surgery were eligible (n = 228). After child discharge, 135 mothers and 98 fathers of 139 children (response rate 61.0%) participated. Six months after surgery, 121 mothers and 92 fathers of 128 children (response rate, 56.1%) took part in the study. INTERVENTIONS: Assessment via a screening instrument and self-rating scale, and extraction of data from charts. MEASUREMENTS AND MAIN RESULTS: The Posttraumatic Diagnostic Scale was applied to estimate self-reported symptoms of PTSD. Following discharge, 16.4% of mothers and 13.3% of fathers met diagnostic criteria for acute PTSD. Another 15.7% of mothers and 13.3% of fathers experienced significant symptoms of posttraumatic stress. Six months after surgery, PTSD rates were 14.9% and 9.5%, respectively. Mothers experienced more severe symptoms of PTSD, but gender differences were not detected with regard to the frequency of PTSD at either time. After controlling for socioeconomic status and child preoperative morbidity, PTSD symptom severity after discharge remained the only significant predictor of PTSD severity at 6 months. Pre-, peri-, and postoperative factors did not predict parental PTSD. CONCLUSIONS: Parents of children undergoing cardiopulmonary bypass surgery are at increased risk for intermediate and long-term psychological malfunctioning. Acute symptoms of PTSD in parents shortly after discharge of their child are a major risk factor for the development of chronic PTSD. Clinicians need to identify parents at risk at an early stage to provide them with systematic support.