To determine the long-term outcomes after multimodality treatment of retroperitoneal, pelvic, and deep truncal sarcomas and to identify the factors associated with local control (LC), distant metastasis (DM), and overall survival (OS). A total of 85 patients with retroperitoneal, pelvic, and deep truncal sarcomas were treated with radiotherapy (RT) between 1987 and 2005. A retrospective analysis of LC, DM, and OS was conducted using log-rank and Cox regression statistical methods. The 2- and 5-year LC, DM, and OS rates were 66% and 51%, 38% and 58%, and 70% and 34%, respectively. Negative surgical margins and a higher radiation dose were associated with greater LC rates on both univariate and multivariate analyses, and female gender was significantly associated with greater LC on multivariate analysis only. None of the analyzed risk factors was significantly associated with DM, although patients with high-grade tumors showed a trend toward an increased risk of DM. Gross residual disease after resection and high tumor grade were associated with worse OS rates on univariate and multivariate analyses, and male gender was significantly associated with worse OS on multivariate analysis only. A time-dependent analysis of LC in relation to DM demonstrated that patients with local failure had a hazard ratio of 19.7 for DM compared with patients without local failure (p < 0.0001). Of the 85 patients, 5 and 8, respectively, had clinically significant acute and late toxicity. The results of this study emphasize the importance of LC in patients with retroperitoneal sarcoma. Radiation dose escalation or radiosensitization strategies to enhance LC are warranted.