The finding, on systemic X-ray examination of a 20-years ol Algerian patient, of an opaque image along the right side of the suprahilar trachea led to the discovery of a rare abnormality of venous return known as azygos continuation of the inferior vena cava. The opacity was ovoid in shape, 4 X 1.7 cm in dimension, well circumscribed and homogeneous. It shrunk during a Valsalva's manoeuvre and increased in size when the patient was lying down. Angiography through the femoral vein showed that the inferior vena cava was interrupted below the liver and continued with the azygos vein. No other cardiovascular abnormality was detected and the situs was normal. Although rare or unrecognized because it is asymptomatic, azygos continuation of the inferior vena cava is the most common of congenital abnormalities of that vessel. It was described initially by Stark in 1835 and remained an anatomical curiosity until 1950. Since the development of vascular opacification techniques, it has been more frequently diagnosed, particularly in children, where it is usually associated with congenital heart disease and/or abnormal situs. Our case is peculiar in that no congenital abnormalities were present.