Postoperative diaphragmatic herniation developed in five patients following transthoracic fundoplication-type hiatus hernia repairs. Three types of hernia resulting from disruption of the diaphragmatic incision, the closure of the hiatal margin, or both have occurred in these patients. Incarceration and symptomatic partial obstruction were associated with volvulus of the supradiaphragmatic portion of the stomach in four patients. One patient developed partial obstruction of a herniated splenic flexure of the colon. An important predisposing factor in the development of these hernias is an insecure closure of the fundoplication to the posterior margin of the hiatal canal. It is suggested that closure of the diaphragmatic incision be made with 2-0 nonabsorbable sutures through all layers and that the fundoplication be sutured to the posterior parietes and preaortic fascia in addition to the crural margin.