In 1992 The International Registry of Inferior Vena Cava (IVC) Leiomyosarcomas was established to study the pathogenesis and natural history of the tumor and to support the most rational treatment. We collected 218 patients through a literature review and personal communications. We corresponded with several Authors to obtain up-to-date follow-up and any other data lacking at the initial review. The series was analyzed to identify predictive factors for clinical outcome. Tumors arose from the IVC lower segment in 80 patients, from the middle in 94 and from the upper in 41. A radical tumor resection was undertaken in 134 (61.5%) patients, 26 (11.9%) had a palliative resection and 58 (26.6%) were inoperable. An increased risk of death was associated with upper IVC segment involvement (p < 0.001), lower limb edema (p < 0.001), Budd-Chiari's syndrome (p < 0.001), intraluminal tumor growth (p < 0.001) and IVC occlusion (p < 0.001). Radical tumor resection was associated with better 5- and 10-year survival rates (49.4% and 29.5%). Tumors which arose from the middle segment fared better (56.7% and 47.3%) than those of the lower segment (37.8% and 14.2%) (p < 0.002). No palpable abdominal mass and abdominal pain were associated, in patients radically operated, with a better outcome and longer survival (p < 0.03 and p > 0.04 respectively). Despite the high rate of recurrence, radical tumor resection is the only long-term cure.