Objective: Our aim was to determine the safety of BAL in young children <6 years with CF. Methods: As part of a multi-center study of BAL-directed therapy, children with CF?<?6 years had one or more BALs between September 1999 and December 2005. Adverse events were recorded intraoperatively and for 24 hr thereafter. Clinical characteristics before BAL, findings at bronchoscopy and BAL results were assessed as risk factors for adverse events. Results: 333 BALs were conducted in 107 (56 males) children, median age 23.5 (range 1.6-67.5) months, including 170 (51%) for pulmonary exacerbation. 29 BALs (8.7%) were followed by fever =38.5àand 10 (3%) had clinically significant episodes (five intraoperative hemoglobin desaturations to <90% requiring intervention, one tachyarrhythmia, two needing post-operative supplemental oxygen, one hospitalization for stridor). Two contaminated bronchoscopes were detected. 180 minor adverse events were recorded in 174 (52%) BAL procedures (137 altered cough, 41 fever <38.5é. Low percentage BAL return (P?=?0.002) and focal bronchitis (P?=?0.02) were associated with clinically significant deterioration. Multivariable analysis identified Streptococcus pneumoniae (OR 22.3; 95% confidence interval (CI); 6.9,72), Pseudomonas aeruginosa (OR 2.4; 95% CI 1.0, 5.8), respiratory signs (OR 5.0; 95% CI 1.7, 14.6) and focal bronchitis (OR 5.9; 95% CI 1.2, 29.8) as independent risk factors for post-bronchoscopy fever =38.5î Conclusions: Adverse events are common with BAL in young CF children, but are usually transient and well tolerated. Parents should be counseled that signs of a pre-existing lower respiratory infection are associated with increased risk of post-BAL fever.