A new-born baby was found to have a duodenal ulcer after developing a severe hematemesis 24 hours after birth. The diagnosis was established by fibroscopic examination, which was also used to follow progress in this case, in which operation for a secondary hypertrophic stenosis of the pylorus led to a favourable outcome. The role of "stress" and, more particularly, gastric hyperacidity in the neonatal period are discussed. Once the critical period is passed, during which hemorrhage and perforation are the cause of the high mortality, recovery is complete.