Chest physiotherapy (CP) is seen as a cornerstone of Cystic Fibrosis (CF) treatment. However, previous studies have suggested that adherence to CP is low. This study of adults with CF (N = 563) investigated CP adherence and associated factors. Only 29.5 per cent reported undertaking daily CP. Predictors of adherence included problems with fitting CP into lifestyle, a perception that CP does not help, physical consequences of CP, doing exercises instead and doing CP as and when necessary. These variables accounted for 45 per cent of the variance in adherence. Content analysis revealed a number of themes related to adherence to CP. Future studies should explore the benefits of daily CP and attempt to devise simple interventions to maximize adherence to CP.