Mortality rate from congenital diaphragmatic hernia (CDH) is still high despite current therapeutic advances. For some time now we have been looking for prognostic parameters which be enable us to determine, in the prenatal and postnatal period, the patients who will die from their pulmonary hypoplasia in spite of treatment and those who will survive. The authors review 94 newborns with CDH diagnosed during the first 24 hours of life. The following prognostic parameters were studied: preoperative arterial gases, position of stomach, right or left sided hernia, liver in thorax and presence of postoperative pneumothorax. All these factors were related to mortality. The arterial gases were the most sensitive factor. Eighty per cent of patients with poor gasometric prognosis died. Thoracic stomach is also a poor prognostic parameter with a 76.7% mortality rate, however we think this does not justify prenatal surgical measures. The remaining parameters were not significant with regard to mortality.