A patient, 5 years of age, presented with a swelling on the right side of the neck. Ultrasonography and computed tomography confirmed a diagnosis of phlebectasia of the right internal jugular vein (IJV). The patient underwent operation and the dilated IJV was excised. Dilatation of the IJV with a Valsalva maneuver suggested a mechanical obstruction in the neck or mediastinum. However, the exact cause is still unknown. Finally, we found the patient to have a thinning of the wall but no other associated abnormality.