Congenital duodenal diaphragm: conversion of stable chronic symptoms to subacute gastric outlet obstruction by penetrating foreign body. Congenital duodenal diaphragms (CDD) are rare lesions that usually become symptomatic and require surgery in childhood. We report a patient, who, although symptomatic since early childhood, had accommodated to the condition and finally required surgical correction in late life after an ingested foreign body traumatized the diaphragm, producing subacute gastric outlet obstruction. The condition, including the reconstruction of the precipitating event, was diagnosed endoscopically prior to surgery. 