BACKGROUND: Gastroesophageal reflux disease (GERD) and chronic rhinosinusitis (CRS) have been shown to be potentially closely related, but the relationship between these conditions, particularly the possibility of a causal link, is not fully understood. This study used Mendelian randomization (MR) to assess the causal relationship between these two disorders. METHODS: We extracted genome-wide association study data sets for GERD and CRS from publicly available gene summaries, and used MR to conduct a causal inference analysis. The main robustness test used in this study included MR-Egger regression, a leave-one-out sensitivity test, and multivariate MR (MVMR). RESULTS: GERD increased the risk of developing CRS by 36%, based on the inverse-variance weighted method, a statistically significant association (odds ratio [OR] 1.360, 95% confidence interval [CI] 1.179-1.568, P < 0.001). Other MR assessment methods, such as weighted median, simple mode, and weighted mode, similarly observed a significant increase in the risk of CRS occurrence (OR 1.434, 95% CI 1.186-1.734, P < 0.001; OR 1.927, 95% CI 1.166-3.184, P = 0.013; and OR 1.910, 95% CI 1.222-2.983, P = 0.006, respectively). No significant bias was found in the heterogeneity or pleiotropy tests (P = 0.071 and P = 0.700, respectively). Even after excluding possible mediators using MVMR, GERD appeared to significantly increase the risk of developing CRS (OR 1.013, 95% CI 1.008-1.023, P = 0.002). CONCLUSIONS: This study provides new, significant evidence that GERD is genetically associated with a higher incidence rate of CRS. However, further research is needed to elucidate the potential underlying biological mechanisms of this relationship.