OBJECTIVES: a) To assess the efficiency of preoperative stabilization with the use of high-frequency oscillatory ventilation in the treatment of congenital diaphragmatic hernia; b) to determine early prognosis factors. DESIGN: Prospective, consecutive patient study. SETTING: A tertiary neonatal intensive care unit in a university hospital. PATIENTS: All patients admitted to the neonatal intensive care unit with a diagnosis of congenital diaphragmatic hernia between April 1990 and June 1993 (n = 18). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Eleven infants had an antenatal diagnosis. Ventilatory settings, blood gas values, arterial-alveolar oxygen ratio, and oxygenation index were recorded on admission and every 3 hrs thereafter until surgery. Surgery was performed if the FIO2 was < 0.3 and mean airway pressure was approximately 9 cm H2O, while the infants were ventilated with high-frequency oscillation. Mean duration of high-frequency oscillatory ventilation was 57 +/- 52 hrs before surgery and 60 +/- 104 hrs after surgery. Overall survival rate was 72%. Infants were divided into two groups, according to the time of surgery. Group 1 (n = 12) patients were operated on in the first 48 hrs of life; on admission, all group 1 patients had an arterial-alveolar oxygen ratio of > or = 0.3 and an oxygenation index of < or = 10, and all recovered. Group 2 (n = 6) consisted of patients for whom preoperative stabilization was difficult to achieve. One infant died before surgery. Four other infants had congenital malformations and subsequently died. Only one infant survived. In this group, the arterial-alveolar oxygen ratio and oxygenation index on admission were 0.08 +/- 0.05 and 33.2 +/- 14.6, respectively (p < .01 vs. group 1). CONCLUSIONS: a) This study demonstrated the efficiency of preoperative stabilization using high-frequency oscillation in the treatment of congenital diaphragmatic hernia. b) An arterial-alveolar oxygen ratio of > or = 0.3 and an oxygenation index of < or = 10 on admission are associated with a rapidly completed surgical procedure and a good outcome.