Background: Exploring bidirectional causal associations between gastroesophageal reflux disease (GERD) and chronic disease of the tonsils and adenoids and chronic sinusitis, respectively.Methods: We first conducted a TSMR (two-sample mendelian randomization) study using the results of the inverse variance weighting method as the primary basis and bidirectional MR to rule out reverse causation. Subsequently, MVMR (multivariate MR) analysis was performed to identify phenotypes associated with SNPs and to explore the independent effect of GERD on two outcomes. Finally, we calculated MR-Egger intercepts to assess horizontal polytropy and Cochran's Q statistic to assess heterogeneity and ensure the robustness of the study.Results: For each standard deviation increase in genetically predicted GERD rate, there was an increased risk of chronic disease of the tonsils and adenoids (OR 1.162, 95% CI 1.036–1.304, P: 1.06E−02) and of developing chronic sinusitis (OR 1.365, 95% CI 1.185–1.572, P: 1.52E−05), and there was no reverse causality. Causality for TSMR was obtained on the basis of IVW (inverse variance weighting) and appeared to be reliable in almost all sensitivity analyses, whereas body mass index may be a potential mediator of causality between GERD and chronic sinusitis.Conclusion: There is a causal association between GERD and chronic disease of the tonsils and adenoids and chronic sinusitis, respectively, and the occurrence of GERD increases the risk of developing chronic disease of the tonsils and adenoids and chronic sinusitis.