Microorganisms are hypothesized to contribute to the pathogenesis of bronchopulmonary dysplasia (BPD) in very low birth weight (VLBW) infants. This hypothesis remains controversial. We sought to determine whether endotracheal colonization with Ureaplasma sp., adenovirus, or Chlamydia sp. increases the risk of BPD. Intubated VLBW infants were included. Polymerase chain reaction (PCR) analysis was used to detect Ureaplasma sp., adenovirus, and Chlamydia sp. The outcome measure was BPD or death due to lung disease. Detection of microorganisms was compared between subjects with and without BPD. Logistic regression was used to control for covariates. Of 139 subjects, 33 (25%) screened positive for Ureaplasma sp., 22 of 136 (16%) were positive for adenovirus; eight of 133 (6%) were positive for Chlamydia sp. At 36 wk postmenstrual age, 14 patients had died, 68 (57%) had BPD. Detection of Ureaplasma sp. was associated with BPD or death (p < 0.001); adenovirus (p = 0.52) and Chlamydia sp. (p = 0.33) were not. Controlling confounding factors, the odds ratio for Ureaplasma sp. and BPD or death was 4.2 (95% CI 1.03, 17). In our population, detection of Ureaplasma sp., but not adenovirus or Chlamydia sp. was associated with BPD or death due to lung disease.