Objective:  Gastroesophageal flap valve (GEFV) grade predicts severe gastroesophageal reflux disease in Caucasians, but its role in other populations is unclear. This study evaluated the significance of endoscopic grading of the GEFV in Taiwanese subjects. Methods:  Five hundred and six consecutive patients undergoing routine check‐ups at the National Taiwan University Hospital were enrolled. Symptoms of upper gastrointestinal disease and endoscopic severity of esophageal mucosal injury were correlated to GEFV grades according to the Hill classification. Results:  The frequency of abnormal valves (Hill grades III or IV) was 27.3%. Of these, 42.7% had erosive esophagitis (EE). The majority of patients with EE were classified as Los Angeles grades A and B (79.7 and 16.9%, respectively). The prevalence of EE, hiatal hernia and, to a lesser degree, non‐erosive reflux disease, increased with altered GEFV. Patients with abnormal valves were younger and more likely to be male, overweight, and to have atypical and extraesophageal symptoms. Conclusions:  Taiwanese patients with abnormal GEFVs share similar characteristics and risk factors with the patients who have EE. Endoscopic grading of the GEFV is highly associated with GERD, and in particular EE, in subjects undergoing routine endoscopy.