Central venous catheter (CVC)-induced hydrothorax is a delayed complication after the placement of an indwelling subclavian or internal jugular central venous catheter. The catheter tips may cause long-lasting mechanical damages that lead to a slow erosion of the wall of the superior vena cava (SVC), thereby resulting in hydrothorax. The damage may stem from the catheter tips being positioned inappropriately or from the relocation of the catheter tip that was initially ideally positioned. We describe an 80-year-old woman with CVC-induced hydrothorax. She presented with spinal subdural hematoma and preoperatively underwent a multiple-lumen CVC insertion through her left subclavian vein. Her recovery course was uneventful after surgical hematoma removal and spinal cord decompression. However, thirty hours after the CVC placement, the patient began to suffer from an increasing dyspnea. The chest X-ray showed right-sided, massive pleural effusion and a widened mediastinum, requiring the removal of the CVC and the drainage of the pleural fluid. After these procedures, the respiratory status improved rapidly. The present case report suggests that the complication of a hydrothorax may occur after a patient's position changes, and it usually occurs in cases where the catheter tip was initially placed in the ideal position. Operators responsible for CVC placement have to be aware of this delayed complication and have the catheter tips remain in a consistently appropriate position.