The relationship between the proximal margins of the gastric mucosal folds and the squamocolumnar mucosal junction (SCMJ) in normal subjects and in patients with columnar-lined esophagus (CLE) was studied. Results indicate that in the normal esophagus, the SCMJ is located within 2 cm of the proximal margin of the gastric folds. The proximal margin of the gastric folds in a hiatal hernia pouch provide a fixed, reproducible, anatomic landmark at endoscopy, which designates the junction of the muscular wall of the esophagus and stomach and permits one to predict the expected normal location of the SCMJ. The diagnosis of CLE should be considered at endoscopy when either the SCMJ is located or columnar epithelium is obtained by biopsy at a site greater than 2 cm above the proximal margin of the gastric folds located within a hiatal hernia pouch. This study provides an endoscopic criterion to permit a more accurate diagnosis of CLE in its earliest stages and may permit a better assessment of its prevalence.