A case in which a patient developed right-sided hydrothorax due to extravasal infusion of total parenteral nutrition (TPN) is reported. The catheter was a triluminal catheter and the tip was shown to be correctly placed in the superior vene cava by x-ray after injection of radio-opaque contrast. The most proximal injection port located 4.5 cm from the tip of the catheter was documented to be sited in the superior mediastinum outside the vena cava. The infusion was given through the proximal port of the catheter. The mechanisms underlying this complication are discussed. The case emphazises the need to control the position of all infusion ports regularly when using central venous catheters with more than one lumen.