Background: Post-traumatic stress disorder (PTSD) in paediatric patients following cardiac surgery has been well reported. Patients with Williams syndrome often require surgical intervention to correct congenital cardiovascular abnormalities and typically present with pre-existing interfering symptoms of anxiety. These patients may be at an elevated risk of developing PTSD following surgical interventions, which has yet to be investigated fully. Methods: In this report, we describe the case of a nine-year-old female with Williams syndrome who developed PTSD following extensive cardiovascular surgery. Results and conclusions: This report details the symptoms and outcome of this specific patient with the intent of educating healthcare providers about this possible risk, as well as some potential treatment and prevention options.