Abstract Topic Benign Disease: Gastro-Esophageal Reflux and Hiatal Hernia Background Ambulatory reflux monitoring off acid suppression is the gold standard for diagnosing gastroesophageal reflux disease (GERD). Barium esophagram (BE) routinely evaluates reflux, but its diagnostic accuracy remains uncertain. We assessed whether BE reliably identifies GERD compared with ambulatory reflux monitoring interpreted using updated Lyon 2.0 consensus criteria. Methods Retrospective analysis of adult patients that underwent BE and ambulatory reflux monitoring (wireless pH or pH-impedance) off PPI within an 8-month interval. Patients with a history of fundoplication were excluded. Esophagram was performed with standard technique and reported by radiology, considered positive for GERD if there was reflux above the thoracic inlet with or without provocative maneuvers. Reflux monitoring studies were considered positive or negative for GERD based on Lyon consensus 2.0 recommendations. Inter-rater reliability, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and received operating characteristic (ROC) curve analysis were calculated for esophagram, with reflux monitoring diagnosis as the gold standard. Results 64 patients were included, 31 % male, mean age = 60 years, mean Body Mass Index = 26. GERD was diagnosed by esophagram in 20 patients (31%), and by reflux monitoring in 19 (30%). Compared to reflux monitoring, BE had sensitivity: 47%, specificity: 76%, PPV: 45%, NPV: 77%, and area under the ROC curve: 0.61 (Figure 1). Inter-rater reliability between BE and ambulatory reflux monitoring was poor (Cohen's Kappa = 0.226). Conclusion There was poor concordance between BE and ambulatory reflux monitoring for diagnosing GERD. BE overall had suboptimal diagnostic performance, with low sensitivity, and moderate specificity. Furthermore, the area under the ROC curve indicates limited ability to distinguish correctly between patients with and without GERD. These findings indicate that barium esophagram should not be relied upon as a diagnostic tool for GERD.