BACKGROUND Congenital diaphragmatic hernia (CDH) with liver herniation and a lung area to head circumference ratio (LHR) < 1 [corrected] is associated with a high rate of neonatal death due to pulmonary hypoplasia. METHODS We report the development of a minimally invasive and reversible fetoscopic tracheal occlusion (FETO) with a balloon, carried out in 21 consecutive fetuses with severe CDH. RESULTS Endotracheal placement of the balloon was successfully performed in all 21 cases and the mean duration of the operation was 20 (range, 5-54) min. The median gestation at FETO was 26 (range, 25-33) weeks. There were no maternal complications such as hemorrhage, placental abruption or pulmonary edema. In 11 (52.4%) patients there was postoperative prelabor amniorrhexis, which occurred within 2 weeks in five patients and after 2 weeks in six patients. Ultrasound scans after FETO demonstrated an increase in the echogenicity of the lungs within 48 h and improvement in the LHR from a median 0.7 (range, 0.4-0.9) before FETO to 1.8 (range, 1.1-2.9) within 2 weeks following surgery. The median gestation at delivery was 34 (range, 27-38) weeks and in 17 (77.3%) patients delivery occurred after 32 weeks. Nine babies died in the neonatal period due to complications from pulmonary hypoplasia. Surgical repair of the diaphragmatic hernia was carried out in 12 babies and in all but one the defect was extensive and required the insertion of a patch. Ten of these babies survived, and at the time of writing were aged 6-25 (median, 18) months and were developing normally. Survival was 30% in the first group of 10 fetuses and 63.6% in the second group of 11 fetuses. The total number of cases was too small for definite conclusions to be drawn as to the causes of this apparent improvement in survival. Nevertheless, improved survival coincided with a shift in the timing of FETO from the third to the second trimester, the administration of epidural rather than general anesthesia, reduced incidence of postoperative amniorrhexis and a change in the policy on the timing of removal of the balloon from the intrapartum to the prenatal period. During the same period of study there were 17 cases examined in the participating centers that met the criteria for FETO but which declined prenatal therapy. In all cases there was isolated left-sided CDH with liver in the thorax and LHR of 0.4-0.9 (mean, 0.7). In five cases the parents elected to terminate the pregnancy. In the 12 cases with expectant management all babies were liveborn but 11 died in the neonatal period due to pulmonary hypoplasia and only one (8.3%) survived. CONCLUSION Severe CDH can be successfully treated with FETO, which is minimally invasive and may improve postnatal survival.