Pneumothorax is the most common complication after central venous catheterization and routinely assessed by a chest X-ray within 4 hours after catheter placement. The diagnosis of pneumothorax may be delayed for hours or days because of minimal clinical symptoms or radiologic signs on initial evaluation. Pneumothorax may progress to tension pneumothorax after positive-pressure ventilation with a potentially fetal outcome. We report a case in which a patient developed a tension pneumothorax while positive-pressure ventilation for general anesthesia 1 day after subclavian vein catheterization, although initial post-insertion chest X-ray was normal.