Leiomyosarcoma (LMS) of inferior vena cava is a rare and aggressive tumor, arising from the smooth muscle cells in the vessel wall. A large complete surgical resection is the essential treatment. The need of vascular reconstruction is not always mandatory. It's above all to understand the place of the reconstruction with artificial vascular patch prosthetics of vena cave after a large resection of the tumor. We rapport two cases of LMS of inferior vena cava in two women who underwent successful large resection of tumor and lower segment of inferior vena cava. In first case, reconstruction of the inferior vena cava was not performed because of the development of venous collaterals derivation. In the second case reconstruction was done using Dacron interposition graft. The necessity of a large resection in management of primary leiomyosarcoma of vena cave makes sometimes unavoidable the sacrifice of a portion of the vena. Indeed, a better comprehension of the development of venous derivation may render unnecessary the reconstruction.