BACKGROUND: The SenseWear Armband (SWA) provides simple and non-invasive measures of energy expenditure (EE) during physical activity, however its accuracy in adults with cystic fibrosis (CF) during free living physical activities has not been established. METHODS: 26 CF adults (mean FEV1 63% predicted; 11 males) completed a series of standardised static and active tasks with simultaneous analysis of EE via the SWA and indirect calorimetry (IC). RESULTS: Mean difference and limits of agreement between EE values from the SWA and IC across all activities were -0.02METs (95% CI -1.1 to 1.1). There was moderate agreement between the two measures (ICC 0.4; 95% CI: 0 to 0.7; p=0.03). For individual activity tasks ICC ranged from 0.1 to 0.6. CONCLUSION: Overall, the SWA demonstrated good agreement with IC for EE estimates in CF adults during a series of free-living activities, however accuracy was variable when assessing EE for specific activities of shorter duration.