An extremely rare case of true brachial arterial aneurysm due to blunt trauma is reported. A 55-year-old male suffered from blunt trauma in his right upper arm when he was 8 years old. He had noticed a mass in his right upper arm for more than 30 years, however, it grew rapidly to 7×6×5cm within several months. Digital subtraction angiography revealed a large saccular aneurysm of the right brachial artery. The aneurysm was removed and replaced by a saphenous vein graft.