BACKGROUND AND STUDY AIMS: The prevalence of endoscopically diagnosed heterotopic gastric mucosa in the upper esophagus (HGMUE) has been reported in a few studies, and varies from 0.1 to 10%. Clinical relevance and possible association with other pathological conditions remain a matter of debate. A prospective study was carried out to determine the prevalence of HGMUE, the influence on it of age and sex, and to study the macroscopic and microscopic aspects of the lesion, its clinical relevance and possible association with other pathological conditions. PATIENTS AND METHODS: A total of 674 new patients with upper digestive complaints or alteration of their state of health underwent upper gastrointestinal endoscopy, with special attention paid to the proximal esophagus when withdrawing the gastroscope. They had been carefully questioned, especially regarding possible complaints, which could have drawn attention to the upper esophagus. RESULTS: Heterotopic columnar epithelium in the proximal esophagus was found in 4.9 % of patients. No difference was observed according to age or sex. A mild to moderate chronic inflammatory infiltration of the heterotopic patch was observed in most cases, not related to the presence in the lesion of Helicobacter pylori, which was found in only one case. Pathological conditions of the gastroesophageal junction, especially esophagitis, were slightly more frequent in patients with HGMUE. Mild complaints, possibly related to the presence of the lesion, were observed in three out of the 33 cases. CONCLUSIONS: On the basis of our prospective study we consider that heterotopic columnar epithelium in the proximal esophagus is a rather common, generally asymptomatic, benign congenital anomaly. Malignant transformation of heterotopic gastric mucosa in the upper esophagus and other severe complications are rare. The need for surveillance should be reserved for the rare cases with metaplasia or dysplasia in the heterotopic columnar mucosa.