Abstract Background and Aims Cystic fibrosis patients are at high risk for chronic kidney disease (CKD), because of chronic aminoglycoside exposure, high protein and dietary salt intake, and Cystic Fibrosis Related Diabetes. Lung transplantation also entails a high renal burden in the long run because of calcineurin inhibitors exposure. We aimed at studying kidney function by gold standard glomerular filtration rate (mGFR) before and 1 year after lung transplantation, as well as identify risk factors for kidney function impairment. Method Patients from the Cystic Fibrosis reference center in Lyon, France were systematically referred to the nephrology department before lung transplantation. mGFR (iohexol or inulin clearance) was performed before and 12-18 months after lung transplantation. Risk factors for a worse nephrological outcome (i.e. post transplantation mGFR < 60mL/min/1.73m²) were searched for. Results 28 patients (10 males), mean age 32 yr, underwent pre transplantation mGFR. Three died following lung transplantation and two progressed to end stage renal disease rapidly thereafter. 23 patients benefited from both pre and post transplantation mGFR. Mean mGFR was 105±21mL/min/1.73m² and 67±19 mL/min/1.73m² before and after transplant respectively. Factors associated with a worse renal outcome in both univariate and multivariate analysis were age at transplantation (p=0.03) and the occurrence of acute kidney injury in the post-operative period (p=0.005). Cumulated aminoglycoside exposure and time spent under cardiopulmonary bypass were not associated with renal outcome. Conclusion Lung transplantation is associated with a high renal burden in adult Cystic Fibrosis patients. We advise a clinical referral to a nephrologist as part of the systematic evaluation in lung transplantation candidates even if GFR is in the normal range.