Background: There are only limited data on the failure patterns after surgical resection for duodenal cancer, and the role of adjuvant chemoradiotherapy (CRT) also remains controversial. In this study, the treatment outcomes of surgery alone were compared to those of surgery plus adjuvant CRT for duodenal cancer. Methods: Between January 1991 and February 2013, a total of 47 patients with duodenal cancer had pancreaticoduodenectomy, and their age ranged from 31 to 80 (median 62). Twenty-five patients (53%) underwent surgery alone, while 22 (47%) underwent surgery plus adjuvant CRT. Postoperative radiotherapy with concomitant 5-fluorouracil was given to tumor bed and regional lymph nodes up to 40–55.4 Gy. Median duration of follow-up was 31 months (range 6–286) for all patients and 90 months (range 14–286) for survivors. Results: CRT (+) group included more patients with advanced nodal stage and overall stage group (p = 0.003 and 0.002, respectively). The 5-year overall survival rates were not different between CRT (−) and CRT (+) groups (50.1 vs. 46.7%, p = 0.794). CRT (+) group achieved a superior 5-year loco-regional relapse-free survival rate compared with CRT (−) group, but the difference did not reach a statistical significance (80.1 vs. 68.4%, p = 0.267). On multivariate analysis, however, the addition of CRT was the only favorable prognosticator predicting loco-regional relapse-free survival (p = 0.046). Two patients experienced grade 3 neutropenia during CRT. Conclusions: Adjuvant CRT after pancreaticoduodenectomy was correlated with an improved loco-regional control in duodenal cancer. Considering the high loco-regional recurrence in surgery alone group, CRT may be considered as adjuvant treatment.