Background: Cystic fibrosis (CF) pulmonary exacerbations (PEx) are associated with significant drop in pulmonary function. The clinical value of measuring bronchodilator (BD) responsiveness during treatment for PEx to monitor or predict recovery of lung function is unclear. Methods: A retrospective analysis of spirometry with BD response testing obtained during hospital admissions for PEx in pediatric CF patients. Repeated events were included for patients with BD testing during multiple admissions. Results: 249 spirometries with BD testing in 102 patients were completed around day 7 (day 4-10) of hospital admission for treatment of CF PEx. Median (IQR) forced expiratory volume in one second (FEV1) was 70.6% predicted (58.1, 84.6) prior to the PEx event (best FEV1 in 6 months prior to admission), 54.4% (41.5, 66.9) at admission, 62.3% (48.4, 74.7) around day 7 of admission and 67.1% predicted (53.8, 78.2) at end of treatment. BD response around day 7 correlated poorly with FEV1 prior to PEx (r=-0.16, p=0.02), and did not correlate with recovery to baseline FEV1 at end of treatment (r=0.08, p=0.22). Only 23/249 (9%) patients had a BD response of ≥12 % and 200 ml. BD response was not related to age or severity of lung disease and led to an immediate change in clinical management in only 4 cases. CONCLUSIONS: BD response in CF patients treated for PEx is poorly correlated with baseline pulmonary function and does not correlate with recovery of FEV1 with treatment. These data suggest that routine testing for BD response is not indicated during PEx.