Objective: Late-onset circulatory collapse (LCC) has been reported that premature babies of more than 7 days old develop circulatory failure in response to glucocorticoid therapy. The aim of this study is to identify clinical factors that increase brain damage in LCC patients. Study design: We retrospectively reviewed total of 167 preterm infants who were born at 35weeks gestation and had hypotension between Apr. 2009 and Mar. 2017 at Seoul Metropolitan Government-Seoul National University Boramae Medical Center. Patients with cardiac diseases including patent ductus arteriosus, confirmed infection, massive hemorrhage, pneumothorax, congenital anomaly were excluded. Forty infants with late-onset hypotension and oliguria after 7days were classified to LCC. We divided the patients into two groups based on ultrasonography and magnetic resonance imaging results; infants with periventricular leukomalacia (n=9) and normal image (n=31) after LCC. The clinical factors including perinatal characteristics, clinical features at LCC period and neonatal morbidities of these two groups were compared. Results: In this study, the incidence of LCC was 6% (n=40). The distribution of LCC infants showed highest at gestational age of 26 weeks (29%) and body weight of 1001-1250g (22%). The incidence of brain damage in LCC patients was 23% (n=9). There was no significant difference in perinatal characteristics and postnatal morbidities between two groups according to brain damage. Postnatal age was older in the group with brain damage (16 vs 24 days, p=0.047). The lowest mean blood pressure (MBP) and the lowest serum sodium concentration were significantly lower in the brain damage group (19 vs 22 mmHg, p=0.034; 125 vs 129 meq/L, p=0.043). There was no significant difference in hypotension duration, oliguria, the highest potassium concentration, cortisol level, inotropic use, hydrocortisone initiation time and duration of the treatment between two groups. Conclusion: Infants with lower serum sodium level and lower MBP during LCC period had more brain damage. Therefore, fast initiation of hydrocortisone and management for normalizing the serum sodium level and MBP are important in LCC patients.