We report a case of bilateral hydrothorax secondary to perforation of the superior vena caval wall, which was caused by a double-lumen central venous catheter used for catheterization of the left jugular vein. A patient undergoing craniectomy developed a right pleural effusion followed by a left hydrothorax 12 hours after the operation. There are several possible explanations for this phenomenon. The horizontal course of the left brachiocephalic vein, heart contraction, mechanical ventilation, changes in patient position, and solutions of high osmolality can promote vascular erosion by the catheter tip. High hydrostatic pressure in the thorax associated with a congenital or an acquired interpleural communication may cause bilateral hydrothorax. We suggest that it is always preferable to cannulate a central vein through the right side. When the left external jugular vein has to be cannulated, an intravascular ECG may be helpful to determine the position of the catheter tip. Chest roentgenogram should be obtained early to confirm catheter position. Furthermore, the distal port of the double-lumen central venous catheter should be used perioperatively for continuous surveillance of the central venous pressure waveform to ensure early warning of venous perforation.