Recent studies show an association between the presence of Ureaplasma urealyticum in tracheal aspirates and bronchopulmonary dysplasia. We hypothesized that among infants with birth weights ⩽1,250 g and respiratory disease, those with U. urealyticum in their tracheal aspirates would have radiographic evidence of more-severe pulmonary disease more often than would those without this organism. A total of 292 low-birth-weight infants who had endotracheal aspirate cultured within 7 days of birth were enrolled. The radiographic outcome variables were pneumonia, early severe bronchopulmonary dysplasia (precocious), and chronic lung disease. Microorganisms were isolated from 128 infants (44%); U. urealyticum was isolated from 44 (15%). Pneumonia was significantly more common in infants with than without U. urealyticum (30% vs. 16%, P =.03). U. urealyticum also was associated with precocious bronchopulmonary dysplasia independent of prematurity, race, and sex (odds ratio, 2.2; P <.05). Tracheal isolation of U. urealyticum within 7 days of birth is associated with pneumonia and precocious bronchopulmonary dysplasia. © 1993, by The University of Chicago.