INTRODUCTION: The remarkable improvement in the long-term prognosis of extremely premature infants has led to an increase in the number of cases of bronchopulmonary dysplasia (BPD). BPD affects pulmonary function and developmental outcomes, resulting in high chronic health burdens for infants and their families over the years. Therefore, identifying its risk factors in the early period of life and exploring better prophylactics and treatment strategies are important.The objectives of our scoping review are to screen available evidence, identify perinatal risk factors involved in the development and severity of BPD and devise a novel disease classification system that can predict long-term prognosis. METHODS AND ANALYSIS: Eligibility criteria are as follows: articles published from 2002 to 2021; studies conducted in developed countries; articles written in English (PubMed) or Japanese (Ichushi); randomised controlled trials, prospective/retrospective cohort studies or case-control studies; extremely premature infants born before 28 weeks of gestational age; and articles in which endpoint was severe BPD as classified by the National Institute of Child Health and Human Development.We will screen the titles and abstracts of studies identified by independent reviewers using the population-concept-context framework. After a full-text review and data charting, we will provide the perinatal risk factors for severe BPD along with the risk ratio or odds ratio, 95% confidence interval and p values. ETHICS AND DISSEMINATION: Institutional review board approval is not required due to the nature of the study. The results of this review will be disseminated through peer-reviewed publications and presentations at relevant conferences.Protocol V.1, 22 September 2021 TRIAL REGISTRATION NUMBER: UMIN000045529.