The study was conducted to evaluate the clinical results of resection for retroperitoneal soft tissue sarcoma (STS) with vascular involvement. The study group consisted of consecutive patients (mean age, 52 years) who underwent surgery for retroperitoneal STS with vascular involvement. The procedures were performed between 1988 and 2004. Vessel involvement by STS was classified as type I, artery and vein; type II, only artery; type III, only vein; and type IV, neither artery nor vein (excluded from the analysis). Patient data were prospectively gathered in a computerized database and retrospectively analyzed. Of 141 patients with retroperitoneal STS, 25 (17.7%) underwent surgery for tumors with vascular involvement. The most common vascular involvement pattern was vein only (type III) at 64%. Arterial and vein (type I) and arterial only (type II) involvement were observed in 16% and 20% of the cases, respectively. STS originating from the vessel wall (primary vessel involvement) was seen in eight patients, and 17 patients had secondary vascular involvement. Resection and vascular repair were done in 22 patients (no vascular repair in three patients due to ligation of the external iliac vein in one patient, and debulking procedures in two). All patients with arterial involvement (type I and II) had arterial reconstruction consisting of aortic replacement (Dacron, n = 3; and expanded polytetrafluoroethylene [ePTFE], n = 2), iliac repair (Dacron, n = 3), and truncal reimplantation (n = 1). The inferior vena cava (6 ePTFE tube grafts, 3 ePTFE patches, 2 venoplasties), iliac vein (1 ePTFE bypass, 1 Dacron bypass, 1 venous patch), and superior mesenteric vein (1 anastomosis, 1 Dacron bypass) were restored in 80% of the patients (n = 16) with either arterial and venous or only venous involvement (type I and type III setting). Morbidity was 36% (hemorrhage, others), and mortality was 4%. At a median follow-up of 19.3 months (interquartile range, 12.8 to 49.9 months) the arterial patency rate was 88.9%, and the venous patency rate was 93.8% (primary and secondary). Thrombosis developed in one arterial and venous (type I) iliac reconstruction due to a perforated sigmoid diverticulitis 12 months after surgery. The local control rate was 82.4%. The 2-year and 5-year survival rates were 90% and 66.7% after complete resection with tumor-free resection margins (n = 10 patients, median survival not reached at latest follow-up). The median survival was 21 months in patients with complete resection but positive resection margins (n = 7) and 8 months in patients with incomplete tumor clearance (n = 8, persistent local disease or metastasis). Patency rates and an acceptable surgical risk underline the value of en bloc resection of retroperitoneal STS together with involvement of blood vessels. The oncologic outcome is positive, especially after complete resection with tumor-free resection margins. A classification of vascular involvement can be used to plan resection and vascular replacement as well as to compare results among reports in a standardized fashion.