Objectives : This study aimed to investigate the current incidence and mortality of massive pulmonary hemorrhage (MPH) among very-low-birth-weight (VLBW) infants in Korea and to assess the risk factors and co-morbidities associated with MPH. MPH was defined as the presence of hemorrhagic fluid in the trachea with acute respiratory failure and/or cardiovascular collapse. Methods : Using the database of the Korean Neonatal Network (KNN), risk factors and co-morbidities of VLBW infants with or without MPH were compared. Included subjects were 5,697 VLBW infants of a total 5,906 KNN cohort born between January 2013 and December 2015. Multivariate logistic regression analysis was performed to assess factors related to MPH. Results : The overall incidence of MPH in the KNN cohort was 6.7% and mortality in the MPH group was 53.3%. In the study group, 372 infants had MPH and 5,325 infants did not. The mean gestational age and birth weight of the MPH group was 26.1 ± 2.38 weeks and 843.9 ± 256.6 g. Multivariate logistic regression analysis demonstrated that MPH was related to birth weight (OR 0.998, 95% CI 0.997-0.999), male gender (OR 1.472, 95% CI 1.119-1.937), multiple gestation (OR 1.284, 95% CI 1.013-1.626) and RDS (OR 9.891, 95% CI 3.032-32.263). Comparing the outcome, BPD (OR 3.144, 95% CI 1.805-5.476), pulmonary hypertension (OR 1.930, 95% CI 1.431-2.601), PDA requiring treatment (OR 1.826, 95% CI 1.421-2.346), IVH (grade III, IV) (OR 2.141, 95% CI 1.598-2.870) and retinopathy of prematurity (OR 1.708, 95% CI 1.210-2.410) were all proven to be associated with MPH. Conclusions : This is the first Korean national report of MPH incidences in VLBW infants and overall incidence was similar to those of other multicenter studies. Lower body weight, male gender, multiple gestation and RDS seem to place VLBW infants at greater risk of MPH and MPH was significantly associated with various co-morbidities of prematurity.