For people interested in risk management, medical activity represents a stimulating field of study and thought. On the one hand, progress in medical kwledge and techlogy tends to reduce the risks to survival that individuals would face in the absence of appropriate diagstic or therapeutic instruments. On the other hand, new medical techlogies simultaneously create their own specific risks, sometimes simply because their effects are less well-kwn than those of established ones. In a sense any medical progress simultaneously generates new risks while destroying old ones. Moreover, unlike many financial risks that can be either divided or transferred to others (e.g. through diversification, insurance or social security) the personal aspects of medical risks are by essence indivisible and n-transferable. As a result, they are in a sense more threatening than financial risks for risk averse patients. These two facts explain and justify the growing interest in risk ecomics for the fields of medical decision making and health ecomics. In Risk and Medical Decision Making, part 1 is developed inside the expected utility (E-U) model and analyses how comorbidity risks affect the well-kwn test-treatment thresholds. Part 2 is devoted to a specific n E-U model with the same purpose: how would one define a threshold in this context and how would one value a diagstic test? In each of these two parts both diagstic and therapeutic risks are considered.