Objectives: To explore preferred treatment decision-making roles, and rationales for role preference, and to identify perceived facilitators to and barriers from attaining preferred role. Design: Qualitative design. Setting and Participants: One secondary care and four primary care sites in North-west England. Purposive sample of 32 adult asthma patients with varied socio-economic backgrounds and disease severity. Methods: Tape-recorded focused-conversation style interviews. Interview topic guide derived from the literature. Sort cards employed to provide the focus for exploration of role preferences. Results: Active (n = 7), collaborative (n = 11) and passive (n = 14) decisional role preferences were identified. Respondents cited level of knowledge; trust; duration of condition; severity of condition at the decisional juncture; lifelong nature of asthma; a perception that 'it is my body'; characteristics of the individual and their response to health professionals as influencing role preference. Perceived facilitators and barriers to participation included condition-related knowledge, practical issues (e.g. lack of time during consultation) and clinicians' interpersonal skills. Conclusions: Most respondents wished to contribute to or feel involved in treatment decision-making, but not necessarily to control it. Some hindrances to participation would be amenable to intervention. The quality of the provider-patient relationship is central to facilitating participation.