Pulmonary complications occur frequently after hematopoietic stem cell transplantation (HSCT) and account for considerable mortality when associated with respiratory failure. Bronchoalveolar lavage (BAL) is commonly used in the diagnostic evaluation of pulmonary infiltrates in HSCT patients. Although the yield of BAL is well established in this setting, the impact on outcome is controversial. In addition, respiratory failure in HSCT patients is associated with high mortality. To determine if positive BAL predicted less respiratory failure and better survival, a retrospective review (between 1992 and 1998) of all HSCT patients who had bronchoscopy with BAL as part of their diagnostic evaluation for new pulmonary infiltrates was performed. Twenty-one patients met the inclusion criteria. Eleven patients (52%) had a positive BAL, defined as the isolation of infectious microorganisms or pulmonary hemorrhage in the lavage specimen. Most of the positive findings were pathogenic organisms (bacterial, fungal, and viral). Respiratory failure (defined as need for both intubation and mechanical ventilation) occurred in 11 of 21 patients (52%)-8 of 11 (73%) who had positive BAL compared with 3 of 10 (30%) who had negative BAL (P = .09). The overall mortality rate was 11 of 21 patients (52%). All deaths except one occurred as a direct result of respiratory failure. Although this study confirmed the high mortality rate in HSCT patients with respiratory failure, the BAL results were not predictive of outcome.