The most common cause of a neck mass that increases in size on the Valsalva maneuver is laryngocele. Jugular phlebectasia is a congenital dilation of the jugular vein, which is extremely rare in adults, may present similarly. Duplication of the internal jugular vein (IJV), which is usually encountered coincidentally, is another rare anatomic variation. Isolated cases or cases associated with IJV ectasia have been reported. We report on an adult patient with coexisting external jugular phlebectasia and internal jugular duplication on the same side. (C) 2004 Wiley-Liss, Inc.