Chronic lung disease is a respiratory disease that usually evolves from an acute respiratory disorder experienced by a newborn infant. The majority of cases arise from bronchopulmonary dysplasia, which is usually described as a disease subsequent to oxygen and/or ventilator therapy for respiratory distress syndrome in preterm newborns. It is defined by oxygen requirement for at least 28 days. Bronchopulmonary dysplasia is primarily interpreted as a developmental disorder in extremely premature infants in which premature birth and the initiation of pulmonary gas exchange at this early stage appear to interrupt the normal alveolar and vascular growth. At this early developmental stage, even minimal exposure to injurious factors, such as mechanical ventilation, oxygen toxicity, or infection, may interrupt this process. Prevention of chronic lung disease is primarily focused on preventing preterm birth. Other strategies include the use of less invasive mechanical ventilation strategies, surfactant administration, prevention of excess oxygen exposure, caffeine therapy, etc. Management is directed at minimizing further injury and providing an optimal environment to support growth and recovery. Most patients gradually improve as healing occurs and lung growth continues. The aim of this thesis was to present the characteristics of infants born at the Department of Gynecology and Obstetrics, University Hospital Center Zagreb, in the year 2017, who required supplemental oxygen for at least 28 postnatal days. During this period, 41 such infants were born, which corresponds to an incidence of 1%. The majority of newborns were born before 28 weeks of gestation and weighing less than 1000 g. The incidence of bronchopulmonary dysplasia, as well as the severity of the disease, increased with decreasing gestational age and birth weight. Additional risk factors that were observed include intrauterine growth restriction, Apgar score, exposure to oxygen and respiratory support modalities. This descriptive research was carried out on a relatively small sample and therefore it is not reliable in making general conclusions.