Background  There is robust empirical evidence to support clinical decision making in secondary stroke prevention after transient ischaemic attack (TIA) or recovered stroke. However, little attention has been paid to patients’ utilization of this evidence in coming to decisions about their treatment choices. Objective  To examine the use of formal and informal knowledge by patients in making decisions about carotid endarterectomy (CEA) and medical treatment after TIA/recovered stroke. Setting and participants  Twenty participants were recruited from an outpatient vascular surgical assessment clinic in England. Ten were receiving medical treatment alone, and 10 were undergoing CEA after TIA or recovered stroke. Method  Twenty‐eight in‐depth qualitative interviews were conducted. An iterative approach was used whereby emergent themes were further explored in later interviews. Interviews were audiotaped, transcribed and coded. Results  Participants gathered and utilized several types of knowledge in the process of making treatment decisions: Empirical knowledge (e.g. clinical trial findings); Pathophysiologic findings (e.g. results of clinical investigations); Experiential knowledge (e.g. personal experience of stroke); Goals and values (e.g. potential impact on family); System features (e.g. apparent urgency of treatment). Conclusions  In addition to formal evidence, patients use other sources of informal or ‘non‐evidentiary’ knowledge to support their decisions about treatment after TIA or recovered stroke. To enable evidence‐based patient choice, health professionals need to appreciate the diverse types of evidence which patients use, to help them to access relevant and high‐quality evidence, to balance evidence from different sources and to make choices which are congruent with their values and expectations.