OBJECTIVE To examine the impact of adjuvant radiotherapy (RT) and surgical technique on survival in retroperitoneal soft-tissue sarcoma. METHODS A retrospective analysis was conducted using the National Oncology Database, a proprietary database of aggregated tumor registries owned by IMPAC(R) Medical Systems (Sunnyvale, CA). Patients who received definitive surgery with negative or microscopic-positive margins were included. Multivariate analysis was performed using the Cox proportional hazards model. Survival curves were estimated by the Kaplan-Meier method and were compared for statistical significance (P < 0.05) using the log-rank test. RESULTS Two hundred sixty-one patients met inclusion criteria. The median follow-up was 59 months (range 0.2-186 months). The 5-year cause-specific survival (CSS) and local failure-free survival (LFFS) were 73% and 66%, respectively. Grade, margin status, and histology were independent predictors for CSS (P < 0.05). Adjuvant RT was associated with a significant improvement in LFFS over surgery alone (hazard ratio = 0.42, 95% confidence interval 0.21-0.86, P < 0.05). Patients receiving simple excision and RT had a 5-year LFFS of 88%, significantly higher than wide resection with or without RT (log-rank, P < 0.05). CONCLUSIONS Adjuvant RT is associated with a lower risk of local relapse compared to surgery alone. The impact of surgical technique on adjuvant RT efficacy warrants further study.