Objective To explore the early clinical manifestations, random cortisol levels, and management of late-onset circulatory collapse (LCC) in preterm infants. Methods Preterm infants with LCC from October to December 2023 at the Affiliated Suzhou Hospital of Nanjing Medical University were included. Maternal perinatal factors and infants' early clinical symptoms, signs, random serum cortisol levels, treatment, and outcomes were retrospectively analyzed. Results Seven preterm infants with LCC were included, with gestational ages of 25 weeks + 2 days to 29 weeks and birth weights of 800-1 150 g. At 3 weeks of age, abnormal weight gain [gain rate: 21-28.5 g/(kg·d)], generalized edema, low serum sodium (129.5-135.2 mmol/L), and decreased random serum cortisol concentrations (13.6-44.6 nmol/L) were observed. After 1-2 weeks of hydrocortisone treatment, edema subsided and serum sodium increased. Conclusions In clinically stable preterm infants, early manifestations of LCC include abnormal weight gain, generalized edema, recurrent hyponatremia, and decreased random serum cortisol concentrations. Hydrocortisone treatment effectively improves symptoms.