Background: With recent advances in systemic therapies and increased survival of patients with metastatic rectal cancer, the role of primary tumor resection may be of increased importance and is often debated. However, the role of combining radiotherapy to surgical resection in the metastatic setting is unknown. Accordingly, we utilized the NCDB to quantify survival in metastatic rectal adenocarcinoma patients with primary tumor resection with and without pelvic radiotherapy. Methods: Of the 15,643 Stage IV rectal adenocarcinoma patients receiving chemotherapy from 2004 to 2014, 4051 patients had primary tumor resection with sufficient follow up for analysis. Patients were stratified by receipt of pelvic radiotherapy (n = 1882) or no pelvic radiotherapy (n = 2169). Univariable/multivariable analyses and propensity-adjusted Cox proportional hazard ratios for survival were performed. Results: Median age was 63 years (18-90) with median follow up of 32.3 months (3.02-151.29). There were more patients with T3/T4 disease (69.6% vs 46.5%) or N1 disease (41.5% vs 27.3%) in the surgery plus radiotherapy arm. Metastatic burden was confined to one organ in 40.5% of patients and was equally distributed between radiotherapy and non-radiotherapy groups (OR 0.92; 95%CI 0.81-1.04). Median survival was 46.3 months vs. 35.3 months in favor of adding radiotherapy (p < 0.001). The 2, 5 and 10-year overall survival were 68.4%, 24.8%, and 9.5% for surgical resection alone compared to 77.2%, 39.6%, and 22.3% for surgery + radiotherapy. On multivariable analysis radiotherapy was associated with a statistically significant reduction in the risk of death (HR 0.718; 95% CI 0.661-0.780). This benefit was upheld on propensity matched analysis (HR 0.722; 95% CI 0.0665-0.784). Conclusions: Our study indicates that adding radiotherapy to surgical management of the primary tumor in patients receiving systemic chemotherapy for metastatic rectal adenocarcinoma improves survival. Prospective investigation of the management of the rectal primary tumor with chemotherapy, pelvic radiotherapy, and surgical resection is warranted.