Background <p>The smooth muscle at the gastroesophageal junction plays a key role in reflux prevention with the clasp and sling fibers contributing to this function. This study aimed to investigate whether gastric subepithelial lesions located within the trajectory of clasp and sling fibers impact reflux esophagitis.</p> Methods <p>From 2013 to 2023, 3002 patients with gastric subepithelial lesions were identified. Patients were divided based on lesion location: within the clasp and sling fiber trajectory (clasp-sling fiber group) or outside (non-clasp-sling fiber group). Demographic characteristics were compared. Propensity score matching and multivariable logistic regression were employed to compare the prevalence and severity of reflux esophagitis between the groups.</p> Results <p>Reflux esophagitis prevalence was higher in the clasp-sling fiber group versus the non-clasp-sling fiber group both before (13.0% vs. 10.6%, <i>P</i> = 0.039) and after matching (13.2% vs. 9.5%, <i>P</i> = 0.005). Multivariable logistic regression showed that the clasp-sling fiber group had higher odds of reflux esophagitis (OR, 1.466; 95% CI 1.160–1.854; <i>P</i> = 0.001). Among matched patients with reflux esophagitis, Los Angeles grades in the clasp-sling fiber group were A 82&#xa0;(53.2%), B 69 (44.8%), and C 3&#xa0;(2.0%); in the other group: A 76&#xa0;(68.5%), B 33 (29.7%) and C 2&#xa0;(1.8%) (<i>P</i> = 0.035).</p> Conclusions <p>Gastric subepithelial lesions within the clasp and sling fiber trajectory are associated with a higher prevalence and more severe grade of reflux esophagitis compared with lesions located elsewhere.</p> Graphical abstract <p></p>