The prenatal diagnosis of pulmonary sequestration has been demonstrated in 17 published reports, including a new case report presented here. In 11 cases (65 per cent), the definitive diagnosis was not appreciated until after birth, although a fetal mass was recognized on ultrasonographic study in the antenatal period. Seventy-five per cent of cases were thoracic sequestrations, and 25 per cent were abdominal lesions. Fetal hydrops, found in 35 per cent of cases, was universally associated with stillbirth or neonatal death. Polyhydramnios, pleural effusions, mediastinal shifts, pulmonary hypoplasia, and preterm labor were not uncommon findings. The high incidence of related malformations, well described in the postnatal literature, was remarkably absent in this antepartum series. Although the perinatal outcome for abdominal lung sequestrations is reasonably good, the prognosis in cases of thoracic sequestration remains guarded. Aggressive respiratory support after birth will not salvage those infants with underlying severe pulmonary hypoplasia. Early in utero catheter drainage may provide the best treatment for the pleural effusions associated with thoracic sequestrations, although this therapy remains under investigation.