Central venous cannulation via an internal jugular vein has become a common procedure in the management and monitoring of severely ill patients. Although complications such as carotid artery puncture or pneumothorax have been reported, hemothorax is relatively uncommon. We describe a case of hydrohemothorax and subclavian artery laceration which occurred during right internal jugular vein cannulation. A 44-year-old female patient was admitted for laparoscopic adrenalectomy under general anesthesia. For central venous pressure monitoring, central venous cannulation performed. However, dilator overinsertion injured the right subclavian artery. This led to a massive ipsilateral hydrohemothorax requiring thoracotomy for subclavian artery repair. This case suggests that central venous cannulation should be done carefully and improves awareness of the potential for dilator induced injury.