Diaphragmatic eventration is a rare entity in the adult population, and usually asymptomatic 1 ; our case is a young man with severe right-sided diaphragmatic eventration with huge dilated colon that has compromised the right hemithorax and caused complete lung collapse and mediastinal shift similar to tension pneumothorax picture with haemodynamic alteration. A single similar case report had been published but did not shed the light on the accurate description of the pathophysiological mechanism of the disease. We believe that such a high abdominal pressure that has transmitted to the thoracic cavity due to the pliable diaphragm causing such a derangment in both the anatomy and the physiology deserves reporting and we think that the term ‘thoracoabdominal compartment syndrome’ describes it accurately, so we discuss some learning points from our case and things that could have been done better.