OBJECTIVES Prior work has found that a doctor's clinical reasoning performance varies on a case-by-case (situation) basis; this is often referred to as 'context specificity'. To explore the influence of context on diagnostic and therapeutic clinical reasoning, we constructed a series of videotapes to which doctors were asked to respond, modifying different contextual factors (patient, doctor, setting). We explored how these contextual factors, as displayed by videotape encounters, may have influenced the clinical reasoning of board-certified internists (experts). Our purpose was to clarify the influence of context on reasoning, to build upon education theory and to generate implications for education practice. METHODS Qualitative data about experts were gathered from two sources: think-aloud protocols reflecting concurrent thought processes that occurred while board-certified internists viewed videotape encounters, and free-text responses to queries that explicitly asked these experts to comment on the influence of selected contextual factors on their clinical reasoning processes. These data sources provided both actual performance data (think-aloud responses) and opinions on reflection (free-text answers) regarding the influence of context on reasoning. Results for each data source were analysed for emergent themes and then combined into a unified theoretical model. RESULTS Several themes emerged from our data and were broadly classified as components influencing the impact of contextual factors, mechanisms for addressing contextual factors, and consequences of contextual factors for patient care. Themes from both data sources had good overlap, indicating that experts are somewhat cognisant of the potential influences of context on their reasoning processes; notable exceptions concerned the themes of missed key findings, balancing of goals and the influence of encounter setting, which emerged in the think-aloud but not the free-text analysis. CONCLUSIONS Our unified model is consistent with the tenets of cognitive load, situated cognition and ecological psychology theories. A number of potentially modifiable influences on clinical reasoning were identified. Implications for doctor training and practice are discussed.