Objective: To verify if the extent of structural lung damage visible on chest CT is correlated with change in ppFEV1 after start of CFTR modulating therapy in CF patients. Methods: In our retrospective observational study, we included patients aged ≥6 years starting ivacaftor or lumacaftor/ivacaftor treatment who were in routine follow up. FEV1 and BMI were recorded every 3 months. From the group of patients who had started lumacaftor/ivacaftor, patients were selected who underwent chest CT within 18 months before or after start of treatment. Patients who had started ivacaftor all underwent chest CT just before the start of treatment. These CT scans were reviewed to determine Brody score. ppFEV1 data was retrieved. To assess correlations, Spearman R and Pearson R tests were applied. Results: Thirty patients met the inclusion criteria, with Brody scores between 0.46-55.30 (median: 19.97, normalized score out of 100) and ppFEV1 before treatment of 19-113 (median: 67). Twenty-three and 7 patients had started lumacaftor/ivacaftor and ivacaftor respectively. Change in ppFEV1 after 6 months of treatment ranged from -19 to +24 (median: +5). For patients using lumacaftor/ivacaftor, the correlation between Brody score and change in ppFEV1 was not significant: Spearman R=-0.213, (p=0.164), but for patients using ivacaftor, there was a significant correlation between Brody score and ppFEV1 change, with a Spearman R=0.679 (p=0.029). Conclusion: The extent of structural damage to the lungs of CF patients is correlated with the response in ppFEV1 to ivacaftor, however this correlation was not demonstrable in patients treated with lumacaftor/ivacaftor.