Purpose: Major venous resection and reconstruction are frequently required during retroperitoneal sarcoma (RPS) surgery for complete oncological resection. However, concerns remain regarding long-term prosthetic venous graft durability, with limited available data. This study evaluated graft patency and reintervention following venous reconstruction during RPS resection. Methodology: All patients undergoing major venous reconstruction during RPS surgery at Sir Charles Gairdner Hospital, Western Australia, between January 2010 and June 2025 were included. Demographic, operative, and follow-up data were collected retrospectively. Primary outcomes were primary graft patency and graft-related reintervention. Results: 36 venous reconstructions were performed. IVC reconstruction was most common (n=26), followed by iliocaval (n=5) and iliac vein reconstruction (n=5). Polytetrafluoroethylene was the predominant conduit (88.9%). Median caval graft diameter was 20 mm (16-24 mm). Over a median follow-up of 35.8 months, five graft occlusions occurred (13.9%), four (80%) within six weeks postoperatively. Kaplan-Meier estimated freedom from graft occlusion was 88.7% at 1 and 3 years (95% CI 78.9–99.8%), and 79.8% at 5 years (95% CI 63.0–100%). Iliocaval reconstructions had a higher observed occlusion rate than isolated IVC reconstruction (40% vs 11.5%), although this did not reach statistical significance. Four graft-related reinterventions were performed (11.1%), two for thrombosis and two for graft kinking. Discharge anticoagulation included rivaroxaban (n=18), apixaban (n=12) and warfarin (n=2), with no association with graft occlusion. Conclusion: Major venous reconstruction during RPS surgery demonstrates favourable long-term durability, with approximately 80% primary patency at five years. Most occlusions occurred within six weeks postoperatively, indicating an early period of increased risk. These findings highlight early thrombosis prevention as a key target for future research.