The growth of simulation technology has brought about rapid innovation in medical education systems. The task of developing and programming these systems is complex. To simplify the process, we developed a typology of medical simulators which allows critical elements to be identified and characterized. The analysis identifies the patients, the procedure, the physician, and the professor as essential elements in any medical education simulator. The level of interactivity of these elements determines the "realism" of the simulator. The development of a fully interactive simulator for ultrasound education will be presented.