Articles about medical decision-support systems often begin with a disclaimer such as “despite many years of research and millions of dollars of expenditures on medical diagnostic systems, none is in widespread use at the present time”. While this statement remains true in the sense that no single diagnostic system is in widespread use, it is misleading with regard to the state-of-the-art of these systems. Diagnostic systems, many simple and some complex, are now ubiquitous and research on these systems is growing. The nature of medical decision-support systems has diversified over time. The prospects for adoption of large-scale diagnostic systems are better now than ever before, due to enthusiasm for implementation of the electronic medical record (EMR) in academic, commercial, and primary care settings. Diagnostic decision-support systems have become an established component of today’s medical technology. In fact, they offer the most attractive way to handle the vast information load that physicians face.