Objective: To describe the characteristics of sustained improved nutritional outcomes through the use of quality improvement (QI) methodology. Design: Retrospective analysis of a QI intervention in two institutions, implemented as part of larger national collaboratives. Setting: Paediatric cystic fibrosis (CF) programmes in academic centres in Alabama and Illinois. Participants: All paediatric patients enrolled in the CF Foundation (CFF) Patient Data Registry were included. Interventions: Improved and sustained nutrition outcomes occurred through implementation of the CFF practice guidelines for CF nutrition management via care delivery processes, nutritional interventions, team engagement and data display. Measurement: Mean body mass index (BMI) percentile, percentage of patients less than 50th percentile and percentage less than 10th percentile for all patients aged 2-20 years were tracked through run charts and statistical process control charts. Mann-Whitney U and X2 tests were used to determine significance between each centre and national outcomes. Results: Each centre achieved rapid improvement in mean BMI percentile in patients, one centre rising from the 40th percentile in 2001 to the 49th percentile in 2003, the other rising from the 37th percentile in 2003 to the 45th percentile in 2004. These centres have also maintained improved nutritional outcomes, so that they were at the 60th and 55th percentiles, respectively, in 2011. Sustained improvement was accomplished through QI methodology, use of data as a driver for improvement and a change in culture. Conclusions: Participation in collaboratives led to improved nutrition outcomes while a strong culture of QI facilitated sustained improvement.