Background: People with Cystic Fibrosis (PwCF) have decreased exercise capacity and quality of life (HRQoL). Since 2020 third generation CF transmembrane conductance regulator modulator, Elexacaftor, Tezacaftor, Ivacaftor (ETI) was approved for PwCF from the age of 12 in Denmark. The results of the treatment over short time show among other increased FEV?, HRQoL and BMI. The effect regarding the new treatment is to date not fully evaluated especially not regarding exercise capacity. Objective: To evaluate exercise capacity using gold standard objective measure, Cardio Pulmonary Exercise Test (CPET) and HRQoL in a cohort of Danish PwCF after more than a year of receiving treatment with ETI. Method: Retrospective cohorte including people with CF from the age of 12, receiving ETI for more than a year. CPET and CFQ-R is performed at baseline and follow-up. Statistics are presented including paired sample t-test. VO? peak (ml/kg/min) and VO? peak (ml/min) and scores from CFQ-R will be evaluated. Results: 156 PwCF performed CPET. Mean follow-up time 15 month (10-22 month), median age 28, 51% female and 59% with chronic infections. Mean BMI and FEV?% pred at baseline 22.0 and 74% respectively. Mean VO? peak (ml/kg/min) at baseline and follow-up 31.9 and 32.5 respectively. Mean diff 0.6, 95% CI [0.008; 2.00], p = 0.05. Mean VO? peak (ml/min) at baseline and follow-up 1972.5 and 2138.3 respectively, mean diff 165.7, 95% CI [124.39; 207.12] p < 0.001. Conclusion: Significant change was shown after 15 month of ETI treatment. The results are preliminary and more results will be presentet ar ERS.