Two cases of congenital duodenal diaphragm were discovered during a review of 2.724 duodenal X-rays performed over the past 3 years. An analysis is made of the total of 40 cases published in the literature. The duodenal diaphragm is a thin wall located into the duodenal lumen with excentric perforation and which undergoes a progressive sacculation. Its embryologic development and close relationship to intraduodenal diverticulum are described. Clinical manifestations are few and unspecific, and the condition can easily be overlooked during surgery even when external palpation or digital exploration of the duodenal lumen is performed following duodenotomy. Special emphasis is placed on the significance of the X-ray images, though they are only orientative when dealing with this condition. Congenital duodenal diaphragm should be kept in mind as a possibility whenever chronic stenosis of the duodenum is diagnosed.