During a five-year period, 32 preterm infants weighing less than 2000 g were diagnosed as having postnatally acquired cytomegalovirus (CMV) infection in a neonatal intensive care unit. These CMV-infected infants were matched with 32 uninfected controls for gestational age, birth weight, and birth date; the two groups did not differ in Apgar scores or the incidence of respiratory distress syndrome and patent ductus arteriosus. Roentgenographic evidence of bronchopulmonary dysplasia (BPD) developed in 24 (75%) of 32 CMV-infected infants, an incidence significantly greater than that observed in control infants (12/32; 38%). Infants with acquired CMV infection required more respiratory support and longer hospitalization than uninfected controls. This association between acquired CMV infection in premature infants and the development of chronic lung disease provides further evidence that vigorous efforts to prevent CMV infection in hospitalized neonates is warranted.