BACKGROUND: Most congenital diaphragmatic hernia (CDH) cases are identified prenatally, enabling early multidisciplinary interventions, including maternal transfer and preparation for extracorporeal membrane oxygenation (ECMO). These strategies may improve the historically stagnant survival rates in Korea. However, multicenter studies on the epidemiology and treatment outcomes of CDH are lacking. This study introduces the Korean CDH cohort (K-CDH), a nationwide prospective registry, and presents interim findings. METHODS: The cohort comprises data from 6 tertiary centers (4 in Seoul and 2 in other regions), all equipped with experienced neonatologists, pediatric surgeons, and ECMO support. Collected data include prenatal characteristics, postnatal management, surgical interventions, and follow-up outcomes. The primary outcome measured was survival to neonatal intensive care unit discharge. Risk factors for mortality or ECMO requirement were also analyzed. RESULTS: Sixty newborns with CDH were enrolled between March 2023 and December 2024. Non-isolated CDH was identified in 16 cases (27%), including three with confirmed genetic syndromes. Sixteen infants (27%) required ECMO, with a mortality rate of 44% among them. In univariate analysis, mortality or ECMO requirement were associated with lower APGAR scores, liver herniation, lower observed-to-expected lung-to-head ratio, and initial PaCO₂, oxygenation index, alveolar-arterial oxygen difference and early severe pulmonary hypertension (PH). Multivariable analysis identified initial PaCO₂ and early severe PH as independent predictors of mortality or ECMO requirement. Among the 57 infants who underwent surgical repair (95%), most had left-sided Bochdalek hernias (n = 47), followed by right-sided (n = 7) and Morgagni-type (n = 3). The median time to surgery of 4 days and 23 (40.4%) required patch repair. Overall, 53% of patients (n = 32) received at least one medication for PH (25 received inhaled nitric oxide and 22 received milrinone). Seven infants were discharged on oral pulmonary vasodilators. The overall survival rate was 85%. CONCLUSION: The interim analysis of the K-CDH cohort demonstrates improved infant survival rates exceeding international benchmarks and confirm that the initial PaCO₂ and severe PH, consistent with previous studies, are predictors of mortality or ECMO. These findings underscore the importance of standardized perinatal care, early risk stratification, and coordinated efforts across multiple centers.