Central vein catheterization is a common procedure for monitoring the central venous pressure, securing vascular access, administrating vasoactive drugs and removing air embolisms. However, many complications can occur, such as vessel injury, pneumothorax, hydrothorax, nerve injury, arrhythmia and infection at the insertion site. We encountered an unusual complication of a localized right hydrothorax that was initially misinterpreted as an atelectasis after left internal jugular vein catheterization and right lateral positioning for a left lower lobectomy.