This article deploys sadomasochism as a framework for understanding medical practice on an institutional level. By examining the case of the factitious illness Munchausen syndrome, this article analyzes the operations of power in the doctor-patient relationship through the trope of role-playing. Because Munchausen syndrome causes a disruption to the dyadic relationship between physicians and patients, a lens of sadomasochism highlights dynamics of power in medical practice that are often obscured in everyday practice. Specifically, this article illustrates how classification and diagnosis are concrete manifestations of the mobilization of medical power.