In November 1987 we began to practice delayed repair of acutely symptomatic congenital diaphragmatic hernia (CDH) following medical and/or extracorporeal membrane oxygenation (ECMO) stabilization. We reviewed 23 consecutive patients with CDH symptomatic at birth treated over the ensuing 2 1 2 years. The mean age at admission, age at repair, and interval from admission to repair were 4.9, 37.0, and 32.6 hours, respectively. Overall survival was 52% ( 12 23). ECMO was used in 14 patients with 7 survivors (50%); 4 of these patients underwent repair prior to ECMO and 10 while on ECMO. The patients were retrospectively grouped into three classes based on postductal arterial blood gas (ABG) response to conventional medical management: class A (n = 8), able to achieve and sustain adequate oxygenation (PO2 > 60 mm Hg) and hyperventilation (PCO2 < 40 mm Hg); class B (n = 10), unable to sustain adequate oxygenation (PO2 < 60 mm Hg) but able to be hyperventilated (PCO2 < 40 mm Hg); and class C (n = 5), unable to be oxygenated (PO2 < 60 mm Hg) or hyperventilated (PCO2 > 40 mm Hg). The interval from admission to repair was 13.6, 53.5, and 25.4 hours for classes A, B, and C, respectively. Two class A (25%), nine class B (90%), and three class C patients (60%) were placed on ECMO. Survival rates were 88%, 50%, and 0% for classes A, B, and C, respectively. We propose the following management protocol. Class A patients are stable and can be repaired at any convenient point after admission without prerepair ECMO; few will need it afterward. Patients in class B are fairly stable, and a period of time can be spent trying to improve their oxygenation with maximal conventional medical management; without improvement, ECMO is instituted, and they undergo repair on bypass. Class C patients are unstable and should be placed on ECMO as soon as possible with later repair, understanding that their prognosis is poor. © 1992.