Abstract: BACKGROUND: Persistent pulmonary hypertension is a problem that leads to high morbidity and mortality in preterm infants. In clinical studies, oxidative stress (OS) contributes to the development of pulmonary hypertension (PH). The most specific biomarker of OS in preterm infants is urinary 8-hydroxy-2-deoxyguanosine (8-OHdG).The aim of the study was to determine the clinical correlation between the value of 8-OHdG and the level of a mean pressure in the pulmonary artery (mPAP) in premature infants with respiratory distress syndrome (RDS) and asphyxia in the early neonatal period. METHODS: Determination of the urinary 8-OHdG value and PH in 96 premature infants born at gestational age of 26–32 weeks on the 1st and the 3rd–5th days of life in two groups: group I –52 children with respiratory distress syndrome; II –44 children with RDS associated with perinatal asphyxia. RESULTS: The 2nd group of children had higher average mPAP level, mmHg, both in the 1st and in the 3rd–5th day of life compared with the 1st group. The value of the urinary 8-OHdG correlated with the manifestation of PH that required prolonged respiratory support in group II. CONCLUSION: Perinatal asphyxia in preterm infants with RDS on the 1st day of life complicates the course of PH, as indicated by a higher level of the urinary 8-OHdG and correlated to mPAP. Gender characteristics of the dynamics of 8-OHdG levels in children with perinatal pathology reveal reduced adaptability and reactivity of boys to OS at birth.