We describe a rare case of hyperplastic polyp of the stomach having its clinical origin in the neonatal period and initially stimulating hypertrophic stenosis of the pylorus. After this neoformation, which almost completely obstructed the pylorus, was endoscopically removed, vomiting ceased and a rapid weight gain was observed. It is known that tumors are a rare cause of gastric outlet obstruction if compared with hypertrophic stenosis of the pylorus. However, our experience suggests that in the case of atypical symptoms, the investigations should be extended, especially to endoscopic examination of the upper digestive tract.