Background: Multiple breath washout (MBW) is increasingly used in the clinical assessment of patients with cystic fibrosis (CF). Guidelines for MBW quality control (QC) were developed primarily for retrospective assessment and central overreading. We assessed whether real-time QC of MBW data during the measurement improves test acceptability in the clinical setting. Methods: We implemented standardized real-time QC and reporting of MBW data at the time of the measurement in the clinical pediatric lung function laboratory in Bern, Switzerland in children with CF aged 4-18 years. We assessed MBW test acceptability before (31 tests; 89 trials) and after (32 tests; 97 trials) implementation of real-time QC and compared agreement between reviewers. Further, we assessed the implementation of real-time QC at a secondary center in Zurich, Switzerland. Results: Before implementation of real-time QC in Bern, only 68% of clinical MBW tests were deemed acceptable following retrospective QC by an experienced reviewer. After implementation of real-time QC, MBW test acceptability improved to 84% in Bern. In Zurich, after implementation of real-time QC, test acceptability improved from 50% to 90%. Further, the agreement between MBW operators and an experienced reviewer for test acceptability was 97% in Bern and 100% in Zurich. Conclusion: Real-time QC of MBW data at the time of measurement is feasible in the clinical setting and results in improved test acceptability.