Background: The standard of care for stage I (T1/2N0M0) rectal adenocarcinoma (RA) is surgery alone. We investigated practice patterns and outcomes associated with administration of radiotherapy (RT) to surgery for stage I RA. Methods: Using National Cancer Database from 2004 to 2015, 11030 patients with clinical stage T1-2N0M0 RA who had definitive surgery were analyzed (7448, definitive surgery alone; 3582, definitive surgery with preoperative or postoperative RT). Between groups, demographic, tumor, and treatment characteristics were compared. Multivariate logistics regression was used to examine factors associated with the receipt of RT. Overall survival (OS) were estimated by Kaplan-Meier method, the log-rank test, Cox proportional hazards models, and propensity score-matched analysis. Results: Of 11030 patients, 33% received RT (58% preoperative, 42% postoperative (only 11 (0.7%) had pathological stage III)); among them, 94.1% received chemotherapy (CT). Patients who received RT tended to be younger, male, diagnosed in early years, covered by Medicare/Not Insured, treated at community cancer program, a lower Charlson score, a T2 clinical stage, a poorly differentiated or a larger tumor. Survival analysis revealed no difference in patients with or without RT (Median survival of 148 vs. 147 months and 5 year OS of 77 vs. 78%, p = 0.12). Multivariate Cox models showed that variables significantly associated with increased hazard of death (p < 0.05) were older age (HR = 1.06), Charlson score 1 (HR = 1.46)/ Charlson score ≥ 2 (HR = 2.14) (vs. Clarlson score 0), pathological III/IV stage (HR = 4.06), Medicaid (HR = 1.68) /Medicare (HR = 1.26)(vs. private insurance), black (HR = 1.28), clinical T2 stage (HR = 1.14) (vs. clinical T1 stage), poor differentiated (HR = 1.32), community cancer program (HR = 1.14) and with larger tumor (HR = 1.001). Propensity score-matched analysis demonstrated a similar 5 year OS (77 vs.76%) in patients with RT or without RT (p = 0.079). Conclusions: One third of stage I RA patients had either preoperative or postoperative RT although addition of RT ± CT did not have a survival advantage and was not recommended. Further studies are warranted to explore reasons for these patterns of care.