Central venous catheters are useful for acute hemodynamic monitoring, fluid resuscitation, drug administration, the aspiration of air embolism and total parenteral nutrition. However, various complications may occur during central venous catheterization and the most common complication of the internal jugular approach is arterial puncture. Arterial puncture can be easily identified by a pulsatile blood flow and the bright red color of blood. It is usually confirmed by connecting catheter to a pressure transducer and observing venous waveforms and venous pressure. We experienced a patient in whom arterial cannulation was unrecognized by pressure recording, but was confirmed by blood gas analysis.