80 cases of pulmonary hypoplasia were found in a review of 956 perinatal necropsies between 1976 and 1983. 63 of these were liveborn but most died on the first postnatal day. 44 were derived from 587 necropsies on inborn patients, representing an incidence of 1.2 per 1000 births. 36 cases were found amongst 369 deaths in infants admitted for care from the region. Hypoplasia was diagnosed on the basis of lung weight and histological maturity in comparison with the body weight and gestational age. 37 cases (46.3%) were associated with a diaphragmatic hernia. In 12 of these pulmonary hypoplasia was unilateral and in 25 it was bilateral. The remaining 43 cases all showed bilateral hypoplasia, 32 in association with major malformation elsewhere, 21 of which were renal. There were 5 cases of bilateral renal agenesis and 7 cystic renal dysplasias. Nonrenal associated malformations included neural tube defects, trisomies and limb anomalies. Bilateral pulmonary hypoplasia with no other malformation occurred in 11 cases (13.8%). Two of these had hydrops fetalis, three were seen with oligohydramnios and one with hydramnios. Such infants are a cause of apparently unexplained respiratory distress in the newborn.