BACKGROUND/AIMS: It has been documented that the Z-line appearance (the ZAP grade) was correlated with the prevalence of intestinal metaplasia. This study was performed to investigate whether there is any correlation between the ZAP grade and the severity of GERD, such as non-erosive reflux disease (NERD) and erosive reflux disease (ERD). METHODS: Consecutive 50 patients with typical reflux symptoms (heartburn and acid regurgitation) and 23 asymptomatic healthy controls were enrolled in this study. The GERD group (n=50) was classified into 2 groups: ERD (n=31) and NERD (n=19). The symptom characteristics were collected by conducting face-to-face interviews with using a structured questionnaire. Endoscopy was performed to determine the ZAP grade and the LA classification. RESULTS: There were significant differences in the ZAP grade among the controls, the NERD group, and the ERD group (p<0.05), although there was no significant difference in age, gender, body weight and smoking history among the three groups. Relatively high correlation was revealed between the ZAP grade and the LA classification (Spearman correlation factor: 0.445). The likelihood ratio to endoscopically diagnose NERD by the ZAP in the patient without reflux esophagitis was 3.66. There were no significant differences in the severity, duration and frequency of symptom according to the ZAP grade. CONCLUSIONS: The ZAP classification may give a clue to diagnosing NERD in the absence of erosive esophagitis, and it could be applied as a useful diagnostic tool for GERD.