Background Gastroesophageal Reflux Disease (GERD) is caused by the reflux of gastric contents into the esophagus and has a 13% global prevalence that is increasing. GERD symptoms negatively impact physical, social, and emotional quality of life. The Frequency Scale for the Symptoms of GERD (FSSG) and the Gastrointestinal Symptom Rating Scale (GSRS) determine the efficacy of treatment but may not correlate with endoscopically estimated esophageal mucosal injury severity. We aimed to probe the correlation between FSSG, GSRS, and esophageal injury severity to evaluate whether these scores can predict GERD severity. Methods A total of 2962 patients who underwent physical examinations, including upper gastrointestinal endoscopy, at the Kyoto Kuramaguchi Medical Center, Japan, were enrolled in this study. Upper gastrointestinal endoscopy was used to diagnose fundic mucosal atrophy, reflux esophagitis based on the Los Angeles (LA) classification, gastroesophageal flap value function (GEFV) based on Hill’s classification, and Barrett’s esophagus. Endoscopic diagnoses were examined for correlations with FSSG and GSRS scores. Results In reflux esophagitis, FSSG and GSRS scores correlated with LA-B and LA-C endoscopic diagnosis but not with LA-M and LA-A endoscopic findings. Multiple regression analysis results were similar. FSSG scores reflected advanced fundic gland mucosal atrophy, while GSRS scores associated with high grade of GEFV. Conclusions This is the first report to examine the correlation between FSSG and GSRS scores and endoscopic findings in a relatively large patient population. Our findings suggest that these scores can diagnose the severity of reflux esophagitis.