A case of congenital, bilateral, diaphragmatic hernia in a patient with multiple trauma after a motor accident is presented. No anamnestic information was available because of the need for intubation at the accident site. After the insertion of bilateral chest tubes because of left sided pneumothorax and right sided haematopneumothorax a mediastinal mass became apparent. A CT scan revealed a bilateral diaphragmatic hernia. Problems and therapy of this condition as well as differentiation between congenital and traumatic hernias are discussed in this case report. A mediastinal mass of unknown origin in multiple trauma patients suggests the presence of traumatic diaphragmatic hernia. Diagnostic signs suggesting congenital hernia as compared to acute traumatic hernia are: unilateral or bilateral localisation in the dorsal muscular part of the diaphragm and non-suspicious appearance of parenchymal abdominal organs in relation to the size of the hernia. Diaphragmatic hernias reduce the vital and functional residual capacity of the lungs, possibly leading to respiratory complications and infections.