Context specificity, or the variation in a participant's performance from one case, or situation, to the next, is a recognized problem in medical education. However, studies have not explored the potential reasons for context specificity in experts using the lens of situated cognition and cognitive load theories (CLT). Using these theories, we explored the influence of selected contextual factors on clinical reasoning performance in internal medicine experts. We constructed and validated a series of videotapes portraying different chief complaints for three common diagnoses seen in internal medicine. Using the situated cognition framework, we modified selected contextual factors--patient, encounter, and/or physician--in each videotape. Following each videotape, participants completed a post-encounter form (PEF) and a think-aloud protocol. A survey estimating recent exposure from their practice to the correct videotape diagnoses was also completed. The time given to complete the PEF was randomly varied with each videotape. Qualitative utterances from the think-aloud procedure were converted to numeric measures of cognitive load. Survey and cognitive load measures were correlated with PEF performance. Pearson correlations were used to assess relations between the independent variables (cognitive load, survey of experience, contextual factors modified) and PEF performance. To further explore context specificity, analysis of covariance (ANCOVA) was used to assess differences in PEF scores, by diagnosis, after controlling for time. Low correlations between PEF sections, both across diagnoses and within each diagnosis, were observed (r values ranged from -.63 to .60). Limiting the time to complete the PEF impacted PEF performance (r = .2 to .4). Context specificity was further substantiated by demonstrating significant differences on most PEF section scores with a diagnosis (ANCOVA). Cognitive load measures were negatively correlated with PEF scores. The presence of selected contextual factors appeared to influence diagnostic more than therapeutic reasoning (r = -.2 to -.38). Contextual factors appear to impact expert physician performance. The impact observed is consistent with situated cognition and CLT's predictions. These findings have potential implications for educational theory and clinical practice.