Bronchopulmonary dysplasia (BPD) is one of the most significant chronic complications of premature newborns treated in neonatal intensive care units. This thesis provides a deep review of the pathogenesis of BPD, the association of hypoxia with the development of BPD associated pulmonary hypertension (BPD-PH), and a discussion of BPD-PH as a whole. Echocardiographic techniques to detect the early presence of BPD-PH are discussed, and a practical demonstration of the signifiance of these echocardiographic values is provided for 4 patients from the department of Pediatrics at the University of Debrecen.