Diaphragmatic defects in cats are common and most frequently occur as a result of trauma. Congenital diaphragmatic defects include peritoneopericardial hernias, hiatal hernias and, infrequently, true diaphragmatic, or pleuroperitoneal, hernias. Only three reports of feline pleuroperitoneal hernias could be found in the veterinary literature. All of these cats presented for evaluation of respiratory distress and two were managed successfully with surgery. This report describes the incidental diagnosis and successfully surgical treatment of a pleuroperitoneal hernia in a cat. It highlights the fact that pleuroperitoneal hernias may not always be symptomatic and that they may not be as rare as previously considered.