INTESTINAL atresia is an uncommon, but highly important condition for the surgeon to recognize early and treat precisely. The term atresia is used to denote complete intrinsic occlusion of the intestinal wall. During the past two decades, there has evolved both a better understanding of the causes of intestinal atresia and a gradual improvement in the results of treatment. In this same period (January 1947 through December 1966) 98 newborns with intestinal atresia have been admitted to the Children's Hospital of Pittsburgh. These form the basis for this review. Only cases of straightforward atresia are included in this paper; cases of stenosis, annular pancreas, or extrinsic obstruction have been omitted. Embryogenesis The etiology of small-bowel atresia is mentioned by Tandler1 in 1900; from a study of the duodenums of 11 human embryos, he first demonstrated the obliteration of the duodenum with the overgrowth of epithelium at the sixth to