Three cases of lung hypoplasia occurring in two siblings and in an unrelated child are reported. All three cases had been exposed to valproate in utero. The two female siblings had no other malformations, whereas the third female had a number of defects consistent with the fetal valproate syndrome. Thus, none of the known major causes of lung hypoplasia was present in any of the three cases. It is discussed whether pulmonary hypoplasia may be a separate disease entity, or caused by prenatal exposure to valproate.