Central venous cannulation via the internal jugular vein or subclavian vein is commonly used in the treatment of critically ill patients. Although arterial puncture and pneumothorax are well-known complications of central venous cannulation, hemothorax, especially when massive, is relatively uncommon. The central catheter passing through a blood vessel into the chest cavity is rare. We present a patient with postpartum hemorrhage who developed a massive hemothorax as a complication of central venous cannulation. She died in the operating room because of intractable blood loss, in spite of vigorous blood and fluid resuscitation. Death was attributed to a massive, untreatable hemothorax and postpartum hemorrhage. We recommend that central venous cannulation should be performed very cautiously, and a chest x-ray must be obtained shortly after the procedure to look for possible complications.