Congenital high airway obstruction syndrome (CHAOS) results in a predictable constellation of findings: large echogenic lungs, flattened or inverted diaphragms, dilated airways distal to the obstruction, and fetal ascites and/or hydrops. The authors report on four fetuses referred for evaluation. None of them survived. Postmortem evaluation showed that three fetuses had laryngeal atresia, and one had tracheal stenosis. Coexistent fetal anomalies were accurately diagnosed by ultrasound in three of the four patients. The finding of CHAOS on prenatal ultrasound examination is diagnostic of complete or near-complete obstruction of the fetal upper airway, most likely caused by laryngeal atresia. A greater understanding of the natural history of CHAOS may permit improved prenatal and perinatal management.