Introduction: Cardio-Pulmonary Exercise Testing (CPET) has been recognized as a valuable method in assessing disease burden and exercise capacity among CF patients.Aim: To evaluate whether colonization status affects Exercise Capacity, LCI and High-Resolution Computed Tomography (HRCT) indices among patients with CF; to check if colonization can predict exercise intolerance.Subjects: Seventy-eight (78) children and adults with CF (31 males) mean (range) age 17.08 (6.75; 24.25) performed spirometry, Multiple Breath Washout (MBW) and CPET along with HRCT on the same day during their admission or follow up visit.Results: 78 CF patients (mean FEV1: 83.3% mean LCI: 10.9 and mean VO peak: 79.1%) were evaluated: 33 were chronically colonized with , 24 were intermittently colonized whereas 21 were free. Statistically significant differences were observed among the three groups in: peak oxygen uptake % predicted (VO peak% ( < 0.001), LCI ( < 0.001), as well as FEV1% ( < 0.001) and FVC% ( < 0.001). colonization could predict VO peak% ( < 0.001, : -0.395).Conclusion: Exercise capacity as reflected by peak oxygen uptake is reduced in colonized patients and reflects lung structural damages as shown on HRCT. colonization could predict exercise limitation among CF patients.