Abstract Background Cough and sputum are major symptoms in cystic fibrosis (CF) that contribute to the impairment of quality of life. Methods This prospective single centre cross-sectional pilot study aimed to evaluate the results of a self-administered questionnaire assessing cough and sputum symptoms (2 domains), and their impact (2 domains) on daily activities in the previous week, named the Cough and Sputum Assessment Questionnaire (CASA-Q) in CF adult patients at stable state, and to analyse associations with clinical, functional, microbiological, radiological data, and two quality of life scales: the Cystic Fibrosis Questionnaire Revised (CFQ-R) and the Saint George Respiratory Questionnaire (SGRQ). Results Forty-eight patients were included in this analysis (69% men; median age of 27.8 ± 8.1 years; median body mass index of 21.8 + 3.3 kg/m²; mean FEV 1 of 64 ± 30% of the predicted value). The mean values of the CASA-Q domains were 58 ± 23 for cough symptoms, 77 ± 24 for cough impact, 62 ± 25 for sputum symptoms and 84 ± 21 for sputum impact. Impairment in CASA-Q cough and sputum domains was associated with dyspnea mMRC scale (p < 0.005 for all 4 domains of CASA-Q) and exacerbations in the previous year (p < 0.05 for CASA-Q symptoms domains). We also found correlations between all domains of the CASA-Q and quality of life questionnaires including SGRQ (p < 0.001) and to a lesser extend CFQ-R. We identified a clinical phenotype (female gender, ΔF508 heterozygous mutation, dyspnea mMRC scale) associated with an impairment of CASA-Q score and quality of life using a 2-step cluster analysis. Conclusions CASA-Q allows the assessment of cough and sputum in CF adult patients and is associated with quality of life impairment. This simple easy-to-use tool could be used in routine clinical practice and in clinical studies to assess cough and sputum in CF patients. Trial Registration The study was registered on ClinicalTrials.gov (NCT02924818, first posted on 5th October 2016).