Traumatic pseudoaneurysms in the head and neck region are very rare. Particularyly, pseudoaneurysms of the internal maxillary artery are known to be very rare. The authors report a 20-year old male who was diagnosed as having a pseudoaneurysm of the internal maxillary artery. The cause was assumed to be a mandible ramus fracture. When he visited our emergency room, we did not consider a pseudoaneurysm because of his other life-threatening conditions. Fortunately, he re-visited our hosipital before the aneurysm ruptured. He was diagnosed with angiography and was treated by using embolization with glue. The rupture of the pseudoaneurysm could have caused a life-threatening hemorrhage.