The discourse of laymen and professionals reveals the dependence of cognition on the interaction between participants, and the limitations of studying expertise by examining isolated individual behavior. This paper examines distributed cognition in the management of Multiple Sclerosis (MS). By varying the level of patient experience with the management of MS, we demonstrate the dependence of physician cognition on the patient’s contribution in four doctor-patient interactions. Experienced patients actively constructed clinical representations and presented initial evaluations for the doctor to refine and validate. Conversations between newly diagnosed patients and doctors demonstrated the physician work to establish a common understanding of the problem and acceptable interventions. Our analysis focuses on the complementary participant roles, and challenges the notion that medical cognition equals physician cognition