The azygos vein may be abnormally situated due to anomalous embryologic development. Its abnormal location is infrequent, but radiologic recognition is much easier than that of the normal vein. This vein, normal or abnormal, becomes distended in conditions with an elevated venous pressure, systemic or portal. Changes in the size of the azygos vein on x-ray are noted to parallel fluctuations of venous pressure. We have demonstrated such changes in a patient with an abnormally situated vein during congestive failure, after recovery, and in various physical positions. X-ray demonstration of such changes can have significant diagnostic application.