The purposes of central venous catheterization (CVC) are as followings, central venous pressure monitoring, pulmonary artery catheterization and monitoring, transvenous cardiac pacing, temporary hemodialysis, drug administration, rapid infusion of fluids, aspiration of air embolism. Various complications may occur during CVC, such as hematoma, pneumothorax, hemothorax, hydrothorax, chylothorax, nerve and artery injury, air embolism, thromboembolism, arrhythmia, heart block, cardiac tamponade, and tracheal puncture. In Korea, several complications have been reported after CVC, such as pneumothorax, hemothorax, hemomediastinum, cardiac tamponade and tracheal puncture. However, there has been no report about the knotting of J-guide wire during the CVC. We report a case of J-guide wire knotting during central venous catheterization.