Simulators that represent human patients are being integrated into medical education. This study examines the use of a haptic-enabled, virtual reality simulator designed to allow training in minimally invasive surgery (MIS) techniques. The paper shows how medical practices and practitioners are constructed during a simulation. By using the theoretical tools that situated learning and communities of practice provide, combined with the concept of reconstituting, I broaden the discussion of medical simulators from a concern with discrete skills and individual knowledge to an examination of how medical knowledge is created around and with computer simulators. The concept of reconstitution is presented as a theoretical term for understanding the interplay between simulators and people in practice. Rather than merely enacting simulator training, reconstituting creates a different context, different actors and different techniques during the simulation. © SSS and SAGE Publications.