Precise staging of reflux esophagitis is very important for therapeutic decisions; in fact, chronic gastroesophageal reflux may cause transmural inflammation that leads to fibrosis with loss of esophageal wall compliance. In reflux esophagitis, endoscopic stating is limited to mucosal injury, while endoscopic ultrasonography (EUS) is able to visualize changes in the layer structure and localized or diffuse thickenings of the esophageal wall. In order to evaluate the usefulness of EUS in reflux esophagitis, a prospective study of 31 patients and ten normal subjects was performed. Endoscopic reflux esophagitis was staged as: E1 (erythema, n = 7), E2 (erosions, n = 13), E3 (ulcers, n = 11). EUS findings were recorded and evaluated at five different levels, starting from the gastroesophageal junction, using a quantitative method, the center line method. With this method, the sectorial and mean thickness, and area were calculated for each level. There was a significant difference between patients with reflux esophagitis and normal subjects in our study. E3 patients showed a significant upward involvement of the wall far from the visible lesions. Mild esophagitis may also cause esophageal wall thickening, involving even the entire wall. There was no correlation between the onset time of symptoms and the degree of thickening. In conclusion, EUS seems to be an important supplement to endoscopy in staging reflux esophagitis, as the progression of the inflammation is not related to the endoscopic findings.