A retrospective study of 2 125 preterm infants, who were ventilated at the Institut de Puériculture in Paris over 9 years (1974-1982) for respiratory distress at birth, showed that 45 (2%) developed clinical and radiological bronchopulmonary dysplasia (BPD): 8 minimal forms, 23 moderate forms and 14 severe forms, 30 of these patients survived (66%). The pathogenesis of this chronic respiratory disease is multifactorial: oxygen + pressure + duration + endotracheal intubation. Efforts should be made to limit the damaging effect of each of these factors, which should be kept down to the minimum values compatible with adequate oxygenation. The presence of emphysema and of a patent ductus arteriosus has also been incriminated, but they may reflect the severity of the initial lung lesion. Rickets, whose incidence was found to be 27%, majors respiratory distress. In the ensuing months, babies with BPD are susceptible to recurrent viral or bacterial respiratory tract infection, failure to thrive and cor pulmonale. The presence of the mother and the care of a psychomotor development specialist are needed for these infants who will be confined for months in conditions which are unsuited to their sensory, physical, emotional and cognitive development.