Congenital posterolateral diaphragmatic hernia continues to be associated with a high mortality from ventilatory failure. To evaluate the malformation and factors associated with survival, 43 children with congenital diaphragmatic hernia seen in the neonatal period were studied; 20 survived. The male:female ratio was 2.1. No consistent antenatal factors could be implicated, and, except for intestinal malrotation and lung hypoplasia, associated anomalies were uncommon. The most common cause of death was ventilatory failure and marked bilateral lung hypoplasia was a common autopsy finding. Most of those died were admitted within 8 hours of birth. Tolazoline has been used in 10 patients since 1975 and, of these, 4 survived. Postoperatively a transient period of satisfactory lung function correlated well with response to vasodilators, which may be of value in future therapy.