To study the accuracy of prenatal diagnosis and define the natural history of fetal congenital diaphragmatic hernia (CDH), we reviewed experience with CDH at The University of California, San Francisco (UCSF) over the last three years. All nine babies born in our institution (inborns) and six of 11 babies referred from other hospitals after birth (outborns) died, an overall mortality of 75%. All had pulmonary hypoplasia. Forty percent had associated malformations or chromosomal abnormalities, a higher incidence than generally reported. Prenatal sonograms were available in all nine inborn cases. CDH was correctly diagnosed prospectively in only five, but could be recognized retrospectively in all nine cases using the sonographic criteria developed from the study. Polyhydramnios was present in all nine cases; in seven cases sonography was performed because the woman was large-for-dates clinically. There were no false positive interpretations, and when necessary the diagnosis was confirmed by amniography. All nine cases of CDH detected in utero died. Seven deteriorated so rapidly that surgical repair could not even be attempted. Two who had optimal care (maternal transport, immediate resuscitation and operation) died after repair despite maximal intensive care including vasodilator therapy. Despite the theoretical advantages of maternal transport to pediatric surgical specialty centers, a majority of fetuses with a prenatal diagnosis of CDH will die because their lungs are inadequate to support extra-uterine life even at term.