The economic evaluation of health technologies, like any pharmaceutical intervention, requires identifying all the resources used in its implementation in the greatest detail possible. The first aspect to be taken into account is the perspective from which the analysis will be made. Obviously, the perspective depends on the target (and audience) of the study. Although society’s perspective is the most suitable one —because it would contemplate all the costs, as society deals directly or indirectly with all the resources— it is not that which is usually used. An alternative option would be that of the agent that finances the health system, which is usually the organisation with most interest in these studies. In the same way, a period of time needs to be defined which is sufficiently long to cover the use of all the resources employed, as well as being able to observe all the associated benefits. However, at the same time, it must be short enough so that the development of the study is affordable. The costs which will be analysed are mainly those associated to the health sector (almost all of them included in what used to be known as direct costs) and to the patient and family members (traditionally known as indirect costs). The former, which are those that are used in all the evaluations, include the medical and pharmaceutical consultations, the laboratory tests and diagnostic procedures, hospital stays of any kind, the products required to care for the patient, etc. The latter, associated to the patient and the family members, include the loss of labour productivity, which in a lot of pathologies takes on an extremely important transcendence. The cost methodology requires an initial identification of all the costs that are relevant so that, depending on the unitary price of each resource, the total value of each of them can be calculated and, finally, the value of the total cost associated to the intervention and to usual care. The difference between the two values found will show the fundamental results: to what extent the implementation of a pharmaceutical intervention affects the cost. A detailed analysis of the uncertainty associated to the parameters is essential.