The concept high sensitivity makes reference to the capability of a system to produce results even when the number of inputs is very reduced (for example, one input). This PhD thesis had several goals: In first place make an analysis of the vast amount of related work which exists about the development of medical diagnosis systems. The second aim was to demonstrate that the application of Semantic Technologies for the creation of a diagnosis decision support system (DDSS) is possible, obtaining accurate results. Also, the problem of multilevel diagnosis (the ability of diagnose a pathology when one of the diagnosis criterions is another pathology) was addressed applying these technologies. Finally, as part of the main aims of the thesis, a new methodology to evaluate this kind of system was proposed.