Question Why do some patients who have received a behavioural graded activity program successfully integrate the activities into their daily lives and others do not? Design Qualitative study. Participants 12 patients were selected according to the model of deliberate sampling for heterogeneity, based on their success with the intervention as assessed on the Patient Global Assessment. Intervention Behavioural graded activity. Outcome measures Data from 12 interviews were coded and analysed using the methods developed in grounded theory. The interviews covered three main themes: aspects related to the content of behavioural graded activity, aspects related to experience with the physiotherapist, and aspects related to characteristics of the participant. Results Interview responses suggest that two factors influence long-term adherence to exercise and activity. First, initial long-term goals rather than short-term goals seem to relate to greater adherence to performing activities in the long term. Second, active involvement by participants in the intervention process seems to relate to greater adherence to performing activities in the long term. Conclusion Although involvement of patients in the intervention process is already part of behavioural graded activity, it would be beneficial to emphasise the importance of active involvement by patients right from the start of the intervention. Furthermore, to increase the success of behavioural graded activity, physiotherapists should gain a clear understanding of the patient's initial motives in undergoing intervention.