Leiomyosarcoma of inferior vena cava (IVC) is a very rare tumor constituting less than 1% of all malignant tumors. However, it is the most common malignant primary IVC tumor. We report a case of primary leiomyosarcoma involving the entire IVC and extending into the right atrium. We also describe a simple endovascular technique that can be used to biopsy IVC masses through a transvenous approach. Our technique can be used as an alternative to percutaneous biopsy which carries a risk of bleeding when transgressing the IVC wall with a biopsy needle. To our knowledge, the use of this technique to biopsy IVC masses has not been described in literature. © SAGE Publications 2011.