Bronchopulmonary dysplasia (B.P.D.) is a condition reflecting the reaction of the immature lung to the intensive support (barotrauma from mechanical ventilation and oxygen toxicity) required for survival in critically ill newborn infants. This study examines all infants who developed B.P.D. over a 2 year period in the Rotunda Hospital. Between 1st January 1986-31st December 1987 there were 1,360 N.I.C.U. admissions, 198 with respiratory problems and 76 requiring assisted ventilation (I.P.P.V.); 23 infants developed B.P.D. with a mean gestational age of 28.7 weeks (SD 2.5), mean birth weight 1,243 g. (SD 523 g.). One infant died at 4 months from S.I.D.S. and one was lost to follow-up (both had been clinically normal). At one year post term the weight was 7,843 g. (SD 1,134) (normal population mean 9.75 Kg. third percentile 8 Kg.) and head circumference 46 cm. (SD 2.5) (normal population mean 47 cm., third percentile 45 cm). During the 1st year of life 11 infants required re-hospitalisation (5 bronchiolitis, 2 urinary tract infections, 2 failure to thrive, 2 myringotomies/grommets) and a further 8 attended hospital with respiratory infections. Only 6/21 received 3 in 1 vaccine (all in hospital O.P.D.) and 14/21 received 2 in 1 vaccine. At one year 15 infants were normal, 2 had cerebral palsy, 2 mild motor delay (one with arrested hydrocephalus), 1 sensorineural deafness and 1 arrested hydrocephalus with mild motor delay. Five infants developed retinopathy of prematurity but none required treatment.