Certain facets of congenital hypertrophic pyloric stenosis (HPS) continue to be controversial. Is the disease really congenital? Wall-gren followed 1,000 newborn males with roentgenologicaly normal stomachs; after three weeks, 5 of these began to vomit and presented the typical roentgenologic signs of HPS. This observed incidence is practically identical to the expected. The clinical onset in the occasional patient within the first few days of life and the reported presence of the disease in the stillborn, however, do suggest prenatal factors. The question may be resolved by recognizing a congenital, inherited anlage for the disease, with the actuating factor (whatever this might be) starting to operate in most cases a variable time after birth, and in a few cases before birth. Is the disease really pyloric? A welter of names has been given the distal few centimeters of the stomach. If use of the name pylorus (gatekeeper) is confined to that ring of circular muscle that guards the entrance to the duodenum...