Background: Adrenocortical carcinoma (ACC) is an aggressive cancer with high recurrence rates and poor prognosis, even after radical surgery. The survival benefit of adjuvant radiotherapy (RT) in patients with ACC has not been well explored. The aim of this study was to evaluate the effect of adjuvant RT on the survival outcome of patients with ACC. Patients and Methods: All patients with nonmetastatic ACC who underwent complete resection were identified from the SEER database (2004–2016). Overall survival (OS) was estimated using the Kaplan-Meier method. Multivariable Cox regression analysis was performed to identify prognostic factors associated with survival. Results: Of 365 patients with nonmetastatic ACC, 55 (15.1%) received adjuvant RT and the remainder underwent surgery alone. Patient characteristics were similar between the 2 groups, but those with a higher disease stage were more likely to receive adjuvant RT. Overall, patients receiving RT seemed to have better survival compared with the non-RT group (3-year OS rate, 63.1% vs 52.8%; P<.062). After adjustment for confounding factors, adjuvant RT was indeed associated with a 48% decreased risk of death (hazard ratio, 0.52; 95% CI, 0.29–0.91; P=.023) for all patients. In addition, adjuvant RT may confer a survival benefit only in patients with a high risk of recurrence (3-year OS rate, 55.1% vs 40.0%; P=.048) rather than in those with low/moderate-risk ACC (P=.559). Conclusions: Our findings suggest that adjuvant RT may be associated with improved survival in patients with nonmetastatic ACC who underwent radical surgery, especially those with high risk of recurrence.