The electronic health record (EHR) is actually an aggregation of individual clinical documents. Medical records document not only the knowledge domains of clinical practice, but the work processes and practices that support these domains. Human-computer interaction is an important factor in EHR system success: researchers have argued that clinician readers consciously perceive the context of production, and integrate an understanding of the producer into their understanding of the data. In support, this paper reports findings of an information retrieval study using a simulated EHR containing deidentified clinical documents. Physician subjects verbally demonstrated use of a mental model of the paper medical record during their navigation of the system. Clinicians may actively apply a mental representation of their domain of practice—and actively refer to this paperbased knowledge base—when they access medical data. An understanding of the mental models that clinicians use would greatly inform our understanding of EHR systems.