The prenatal diagnosis of pulmonary sequestration can usually be made by the third trimester of pregnancy, from the combination of an intrathoracic mass and indirect signs such as cardiac deviation, fetal hydrops, pleural effusion and polyhydramnios. We describe four cases in which pulmonary hyperechogenicity was detected before 26 weeks' gestation. In three cases the hyperechogenic mass was isolated. In all cases it had mostly regressed during the pregnancy. A review of the cases of isolated pulmonary sequestration that have been diagnosed during the antenatal period is presented. Antenatal evolution was found to be unpredictable regardless of the type or severity of the case at the first diagnosis. We propose a classification to define more clearly the optimal management of pulmonary sequestration. Copyright © 1995 International Society of Ultrasound in Obstetrics and Gynecology