Primary vascular tumors such as vascular leiomyosarcomas are rare, but exhibit markedly different characteristics than tumors that invade the vasculature from a secondary source. Establishing a diagnosis is essential in determining the appropriate treatment plan, but obtaining a histologic specimen may prove challenging and carry significant risks. Minimally invasive endovascular biopsy techniques can be pivotal in the diagnosis-and thus in the management-of vascular tumors. We present a case of a primary inferior vena cava leiomyosarcoma, not able to be adequately assessed by noninvasive imaging and deemed too risky to be approached with traditional percutaneous biopsy techniques. Accurate diagnosis of such tumors is critical, as the success of surgical resection, although high risk, depends greatly upon the type, location, and extent of malignancy.