Azygos vein aneurysm is a rare cause of a posterior or paratracheal mediastinal mass. Trauma or conditions causing elevated ﬂow or pressure in the azygos system, such as cardiac failure or cirrhosis of the liver are secondary causes of aneurysm of the azygos vein. We report a case of asymptomatic saccular aneurysm of the azygos vein in a 45-year-old man with blunt minor chest trauma. The azygos vein aneurysm was managed by conservative treatment.