We present a unique case of intercostal muscle flap (ICMF) ossification mimicking an intrathoracic rib diagnosed 3 years after oesophageal perforation repair. A 58-year-old male presented with complaints of mild chest discomfort. Three years ago he had undergone left thoracotomy and primary repair of post-emetic oesophageal perforation. An ICMF had been used to strengthen the repair. Chest X-ray identified a linear calcific density within the left hemithorax. Subsequent thoracic CT characterized the anomaly as ossification of the ICMF. The lesion had the appearance of a well-differentiated intrathoracic rib coursing through the left lower lobe. We discuss the typical appearances of ossified ICMFs and the potential complications resulting from this ossification.