Purpose: Congenital diaphragmatic hernia (CDH) is rare but potentially fatal. The overall outcome is highly variable. This study aimed to identify a simple and dynamic parameter that helps predict the mortality of CDH patients in real time, without inva sive tests. Methods: We conducted a retrospective chart review of 59 CDH cases. Maternal and fetal information included the gestational age at diagnosis, site of defect, presence of liver herniation, and lungtohead ratio (LHR) at 20 to 29 weeks of gestational age. Information regarding postnatal treatment, including the number of days until surgery, the need for inhaled nitric oxide (iNO), the need for extracorporeal mem brane oxygenation (ECMO), and survival, was collected. The highest respiratory se verity score (RSS) within 24 hours after birth was also calculated. Results: Statistical analysis showed that a younger gestational age at the initial dia gnosis (P<0.001), a lower LHR (P=0.001), and the presence of liver herniation (P= 0.003) were prenatal risk factors for CDH mortality. The RSS and use of iNO and ECMO were significant factors affecting survival. In the multivariate analysis, the only remaining significant risk factor was the highest preoperative RSS within 24 hours after birth (P=0.002). The area under the receiver operating characteristic curve was 0.9375, with a sensitivity of 91.67% and specificity of 83.87% at the RSS cutoff value of 5.2. The positive and negative predictive values were 82.14% and 92.86%, respectively. Conclusion: Using the RSS as a prognostic predictor with simple calculations will help clinicians plan CDH management.