Antenatal in utero surgery for congenital diaphragmatic hernia has been justified by reported perinatal mortality rates of 77% to 80%. Such rates may have been subject to bias of ascertainment and may include fetuses with additional severe malformations who would not be surgical candidates. We used the Iowa Birth Defects Registry to conduct a complete population survey to determine the incidence of congenital diaphragmatic hernia, the frequency of associated severe malformations, and the morbidity and mortality of infants with isolated congenital diaphragmatic hernia who were not subjected to antenatal surgery. The incidence of congenital diaphragmatic hernia was 1 in 3715. Twenty-eight percent of affected fetuses had associated severe malformations that were potentially identifiable prenatally and that would have precluded antenatal surgery. Of those with isolated congenital diaphragmatic hernia, 55% survived in spite of delivery (88.5%) and/or surgical repair (44%) in a level I or II hospital. Any decision for in utero surgery to repair congenital diaphragmatic hernia must be based on this or similarly obtained information.