Objectives This study aims to assess how implementing a checklist for managing extremely preterm or extremely low birth weight infants can reduce mortality rates and morbidities. Design A quasi-experimental, before-and-after study. Setting Neonatal intensive care unit at Dr. Cipto Mangunkusumo National General Hospital, a national referral hospital in Indonesia. Participant 86 infants were born at <28 weeks of gestation and/or with birth weight <1000 g. Exclusion criteria were major congenital anomalies incompatible with life. 48 were managed prior to checklist implementation (September 2022–March 2023) and 38 after checklist implementation (April–October 2023). Interventions Implementation of a modified Canberra Health Services extremely preterm-early management checklist during the initial management of extremely preterm or low birth weight infants, including humidified gas resuscitation, thermal management, early surfactant administration and standardised first-hour care protocols. Main outcome measures The primary outcome was the mortality rate. Secondary outcomes included comorbidities such as hypothermia, hypoglycaemia, acidosis, intraventricular haemorrhage (IVH), periventricular leukomalacia (PVL) and retinopathy of prematurity (ROP). Results A total of 86 extremely premature and/or extremely low birth weight infants were enrolled, 48 neonates prior to and 38 neonates after the use of the checklist. Baseline characteristics were comparable between groups (median gestational age 27 weeks in both groups, median birth weight 795g vs 868.5g, p=0.09). Mortality at discharge showed a non-significant reduction from 52.1% to 47.4% (p=0.664, 0.91, 95%CI 0.64 to 1.30). Significant reductions were observed in IVH (79.2% to 28.9%, p<0.001) and ROP (56.3 to 15.8%, p<0.001). No significant differences were found in hypothermia, hypoglycaemia, acidosis rates or PVL. Conclusions Implementation of a systematic checklist was associated with significant reductions in IVH and ROP, though mortality reduction was not statistically significant. These findings suggest potential benefits of structured early care protocols, but the observational design limits causal inference. © Author(s) (or their employer(s)) 2025. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ Group.