Background Bilateral diaphragmatic agenesis (DA) is a rare congenital defect leading to a bilateral herniation of abdominal organs into the thorax cavity [1]. Diaphragmatic defects are often associated with congenital anomalies and genetic syndromes. However, the occurrence of DA in association with Cornelia de Lange (CDL) Syndrome is very rare [2]. Aim To discuss the current diagnosis and treatment options of DA associated with CDL Syndrome. Methods This report describes the case of a male, late preterm neonate with prenatally diagnosed DA and CDL Syndrome. Results The infant presented with severe respiratory distress after birth, bilateral pulmonary hypoplasia, and herniation of abdominal organs into the chest cavity. The postnatal management was performed according to the recommendations of the Congenital Diaphragmatic Hernia EURO Consortium, including immediate intubation and invasive mechanical ventilation [3]. Chest auscultation revealed a decreased air entry, only reaching the upper lungs. Physical examination confirmed congenital malformations associated with CDL Syndrome, including microcephaly, facial dysmorphia with micro- and retrognathia, long philtrum, long eyelashes, and cleft palate. In addition, the x-ray showed bilateral diaphragm agenesis with herniation of the liver, spleen, and stomach into the thorax resulting in pronounced bilateral pulmonary hypoplasia. Despite inhaled nitric oxide, the application of intensive high-frequency oscillatory ventilation oxygenation gradually deteriorated. Due to the unfavorable prognosis, an interdisciplinary consensus was reached to forego extracorporeal membrane oxygenation (ECMO). The boy died at four hours of age. The parents declined an autopsy, photographic documentation, and postmortem computer tomography. Conclusion DA remains a life-threatening disease despite early prenatal MRI diagnosis, comprehensive treatment of respiratory insufficiency, including intubation, lung-protective ventilation, extensive supportive therapy, and ECMO use [4]. Article published online: 06 June 2023 © 2023. Thieme. All rights reserved. Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany