The most common cause of a mass in the neck, which appears only during the Valsalva manoeuvre, is a laryngocele. Less common are venous malformations in the neck, especially in children. We report a 5-year-old boy with a progressively enlarging tumour in the neck that proved to be a malformation between the common facial vein and external jugular vein. Comparable ultrasonography and computerized tomography are the diagnostic methods to distinguish the pathology. Surgical excision was carried out successfully.