To explore preferred treatment decision-making roles, and rationales for role preference, and to identify perceived facilitators to and barriers from attaining preferred role. Qualitative design. 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. 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. 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. 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.