METHODS Forty-five patients were consecutively treated for primary retroperitoneal soft tissue sarcoma with surgery in combination with radiation therapy in the same institution. The median follow-up time was 53 months (7-108). RESULTS Seventeen (38%) patients had clear microscopic margins (R0 resection), 26 patients (58%) had gross complete surgical excision (R1 resection) and two patients (4%) had a macroscopic residual disease (R2 resection). External radiotherapy doses ranged from 40.8 to 59.4 Gy (mean and median: 49 Gy). Seventeen patients underwent intraoperative radiation therapy (IORT). Moreover, 11 patients received chemotherapy. The overall 1-, 2-, and 5-year survival for all 45 patients were 93, 85 and 60%, respectively. The 1-, 2-, and 5-year locoregional relapse-free rate for the whole group was 91, 70 and 40%, respectively. In univariate analysis, quality of surgery was the only variable to show a significant effect for overall survival (P=0.0386) and for local control (P=0.0059). Tumor size and tumor grade had no statistically significant effect. For the patients receiving IORT+external beam radiation therapy, no difference was observed for survival or locoregional control. The most frequent acute side effects treatment complications were radiation-induced nausea or vomiting (42%) and moderate enteritis (30%). Significant late morbidity was observed for two patients. CONCLUSIONS This study confirms the feasibility of external postoperative radiotherapy with an acceptable level of toxicity. However, the high rate of local relapses (especially in field of radiation) does not demonstrate the usefulness of radiotherapy at the level of dose used and further preferably randomized studies should be planned.