Pulmonary infiltrates frequently complicate hematopoietic SCT (HSCT). The utility of fiberoptic bronchoscopy (FOB) with bronchoalveolar lavage (BAL) in the evaluation of new pulmonary infiltrates, particularly as it relates to optimal timing of the procedure, is unclear. Based on this, we retrospectively reviewed 501 consecutive, adult, nonintubated patients who underwent 598 BALs for evaluation of new pulmonary infiltrates during the first 100 days following HSCT to determine whether diagnostic yields for infection, subsequent antimicrobial treatment modifications and patient outcomes differed following early vs late referrals for the procedure. The overall yield of BAL for clinically significant pathogens was 55%. Notably, the yield was 2.5-fold higher among FOBs performed within the first 4 days of presentation (early FOB) compared to those performed late, and highest (75%) when performed within 24 h of clinical presentation. Rates of FOB-guided adjustments in antimicrobial therapy (51%) did not differ significantly between early and late examinations. However, late FOB-related antibiotic adjustments were associated with 30-day pulmonary-associated deaths that were threefold higher (6 vs 18%, P=0.0351). Major FOB-related complications occurred in only three (0.6%) patients. We conclude that early referral for FOB in this patient setting is associated with higher diagnostic yields and may favorably impact survival.