A leiomyosarcoma of the uterus in a 54-year-old woman exhibited striking involvement of large vessels of the myometrium and broad ligament on both gross and microscopic examination. The pattern of vascular involvement resembled that seen in intravenous leiomyomatosis. Imaging studies showed recurrent tumor within the inferior vena cava 3 months after hysterectomy. To our knowledge, this is the first reported such case in the literature, for which we propose the designation intravenous leiomyosarcomatosis of the uterus.