Telangiectases of the legs occur frequently, with most patients seeking treatment for cosmetic reasons. Sclerotherapy continues to gain popularity as a safe and valuable therapeutic approach; however, deep vein thrombosis as well as pulmonary embolism have been reported even after sclerotherapy of small intradermal venectases. Hoping to uncover anatomic risk factors predisposing a patient to iatrogenic thrombosis, we investigated 15 patients with telangiectases of the legs applying ascending venography concomitantly with direct injection of the telangiectases. A digital radiographic technique was used as an imaging system. In two patients an unrestrained flow of the contrast medium into the venae femorales was noticed. As far as we know this is the first in vivo demonstration of venae communicantes connecting intradermal venectases to the deep veins. That means that particular anatomic conditions favor the spillage of sclerosant into the deep veins, which might contribute to the development of iatrogenic deep vein thromboses in compression sclerotherapy.