security) the personal aspects of medical risks are by essence indivisible and non-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 economics for the fields of medical decision making and health economics. 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-known "test-treatment" thresholds. Part 2 is devoted to a specific non E-U model with the same purpose: how would one define a threshold in this context and how would one value a diagnostic test? In each of these two parts both diagnostic and therapeutic risks are considered.