Patches of hererotopic gastric mucosa located in the upper esophagus are a frequent finding at endoscopy. These lesions are thought to be of congenital origin and of low malignant potential. However, several cases of adenocarcinoma developing on inlet patches have recently been described. We report here a new case of adenoma that had developed on heterotopic gastric mucosa in the upper esophagus, associated with an area of high-grade dysplasia. This polyp was removed surgically under endoscopic guidance, after confirmation of the superficial pattern of the lesion by endoscopic ultrasonography. This report emphasizes the malignant potential of esophageal inlet patches of heterotopic gastric mucosa.