Klippel-Trenaunay-Weber syndrome is a rare, sporadically occuring disorder characterized by hemihypertrophy (unilateral limb hypertrophy), varicose veins, hemangiomata and occasionally arteriovenous malformation. With the development of ultrasonography, this syndrome can be detected by antenatal sonography. We report a case of Klippel-Trenaunay-Weber syndrome that demonstrates huge mass with increased blood flow on left thigh detected by ultrasonography.