Fourteen cases of small bowel obstruction caused by congenital or postoperative internal herniation of bowel and treated at the University and Veterans Administration Medical Centers, Jackson, Mississippi between 1970 and 1983 were reviewed retrospectively. Of the total, eight were congenital (three transomental, two paraduodenal, one foramen of Winslow, one ileocecal transmesenteric, and one paracecal) and six acquired (three transmesenteric, one behind a Roux-Y esophagojejunostomy, one behind a Roux-Y pancreaticojejunostomy, and one between limbs of an end colostomy mucous fistula). Gangrenous bowel was present at exploration in nine cases (64 percent, five congenital and four acquired). In no case was a correct preoperative diagnosis of incarcerated or strangulated internal hernia made. In each patient, except for one who died before celiotomy could be performed, reduction of the hernia contents, resection of necrotic bowel, primary anastomosis or, on occasion, enterostomy, and correction of the anatomic defect leading to the herniation were performed. Postoperative mortality was 31 percent (four patients). Each of the four patients had presented initially with gangrenous bowel. The clinical features and management of congenital and acquired internal hernias have been reviewed and correlated with therapeutic outcome. In addition, the difficulties in diagnosis and the features of various types of these hernias have been discussed with comments made regarding prevention of the acquired forms of these rare hernias, along with the embryologic background and methods of management of the various congenital defects.