Central venous catheterization is a frequently performed procedure in the intensive care units (ICU) for various treatments such as iv therapy, parenteral nutrition and hemodialysis but occasionally encountered complications can be fatal. Therefore, safe insertion with confirmation of correct positioning of the catheter is vital. Ultrasound (US)-guided insertion of catheters has been used widely, and its safety and efficacy have been demonstrated in several studies. However, this technique is not free from complications, such as carotid artery puncture, hemothorax, pneumothorax and infection. In this case, anterior mediastinal hematoma proceeded after US-guided internal jugular vein (IJV) catheterization.