We describe herein two cases of vascular malformations, one classified as hemangioma and the other as Klippel-Trenaunay syndrome. Clinical investigation in each case failed to demonstrate the presence of arteriovenous (AV) shunting. Arteriographic findings revealed only indirect evidence of AV shunting in each case. In contrast, systematic scanning with a Doppler ultrasonographic probe of the involved extremities provided evidence of AV shunting and pinpointed it in suspected arteriographic areas. Good correlation between the two methods was confirmed in the hemangioma case both preoperatively and intraoperatively. In the case of Klippel-Trenaunay syndrome, evidence of multiple AV shunts was obtained primarily with Doppler ultrasonography. In addition to arteriography, serial phlebography, when indicated, is also necessary for complete evaluation of concomitant venous malformations. The pathogenic mechanism of these vascular malformations was briefly reviewed, emphasizing AV shunting as a common link between the various anatomicoclinical forms.