ABSTRACT Background Duodenal stump leakage (DSL) is a serious complication in gastrectomy. However, its risk factors remain unknown. Moreover, whether duodenal stump reinforcement can effectively prevent DSL is unclear. Therefore, the present study aimed to identify the risk factors for DSL and to assess the efficacy of duodenal stump reinforcement in preventing DSL. Methods A total of 1918 patients with primary gastric cancer who underwent total or distal gastrectomy with Roux‐en‐Y reconstruction at our institution between 2012 and 2023 were included in this study. Multivariate analysis was conducted to identify the risk factors for DSL and to determine the efficacy of duodenal stump reinforcement in preventing DSL. Results Among the patients, 660 were aged 75 years or older, 1387 were male, and 447 had a body mass index (BMI) ≥ 25. Open surgery was the most commonly performed surgical approach (1121 patients), followed by laparoscopic surgery (540 patients) and robotic surgery (257 patients). DSL occurred in 24 patients (1%). The multivariate analysis showed that overweight with a BMI ≥ 25 and laparoscopic surgery were independent risk factors for DSL, and duodenal stump reinforcement was an independent preventive factor for DSL. Regarding the duodenal stump reinforcement procedure, DSL occurred in four patients (0.6%) who underwent interrupted sutures, but not in those who underwent purse‐string sutures. Conclusion Overweight with a BMI ≥ 25 and laparoscopic surgery were identified as risk factors for DSL in gastrectomy and duodenal stump reinforcement appeared to be effective in preventing DSL.