Congenital diaphragmatic hernia (CDH) is associated with a neonatal mortality of up to 50 per cent resulting from pulmonary hypoplasia. Experimental ligation of the trachea increases pulmonary growth in fetuses with experimental diaphragmatic hernia (EDH). To provide a potentially reversible tracheal occlusion (TO) using a minimally invasive procedure, we designed the endoscopic placement of a latex tracheal balloon in fetal lambs with EDH. Following surgical creation of a left EDH at 85 days' gestation, endoscopic occlusion of the fetal trachea was performed at 120 days. The fetuses were retrieved at 139 days. The procedure was successful in 5/11 attempts, resulting in liveborns in which the balloon occluded the trachea completely with expanded lungs and reduction of the herniated viscera into the abdomen. These cases were compared with five cases of EDH without TO and six controls. In the TO group, the lung weight was significantly greater but the radial alveolar count, DNA content, and protein content were similar to normal controls. All lung growth parameters were greater in the TO than in the EDH group. Occlusion of the trachea using an endoscopic technique could provide a useful alternative to open fetal surgery in fetuses with CDH.