Objective To assess the value and accuracy of gestational age at diagnosis in predicting postnatal outcomes of prenatally diagnosed congenital diaphragmatic hernia (CDH). Study design The medical records of 158 prenatally diagnosed neonates with CDH from 2008 to 2018 were retrospectively reviewed. Data were analyzed using parametric and nonparametric tests, appropriately. Results Gestational age at diagnosis predicted postnatal survival independently. Survival rate at discharge increased when gestational age at diagnosis increased (p < .001). Area under the receiver operator curve for survival for gestational age at diagnosis was 0.74, observed-to-expected lung to head ratio 0.74, and liver herniation 0.76. Patients diagnosed with CDH before 25 gestational weeks had a larger size of the diaphragmatic defect, more need for patch repair, longer duration of mechanical ventilation and hospital stay than those after 25 gestational weeks. Conclusions Gestational age at diagnosis is an independent predictor of CDH prognosis. It has a similar ability to predict survival compared to observed-to-expected lung to head ratio and liver herniation.