A 63-year-old woman successfully underwent a graft replacement of the retrohepatic inferior vena cava with a ringed polytetrafluoroethylene graft for primary leiomyosarcoma of the inferior vena cava (IVC). Although anticoagulant had been administered, a thrombus was found in the IVC just cranial of the downstream anastomosis 67 months after the operation. The patient remained free of symptoms, and she had no evidence of any tumor recurrence. She underwent a complete resection with a prosthetic reconstruction for leiomyosarcoma of the IVC and has since been able to enjoy a reasonably long-term survival. The occurrence of thrombosis must be kept in mind in the long-term follow-up of such cases.