Intravenous leiomyomatosis is a rare, histologically benign neoplasm that may be malignant in its specific tendency to intravascular extension. A case of intravenous leiomyomatosis with extension into the entire inferior vena cava in a 41-year-old woman is described. The patient was diagnosed with syncope 3 years after hysterectomy and was treated with a 1-stage procedure including venous replacement.