The Republic Constitution of 1988 expressly forbade the possible use of illegal evidences in all proceedings (art. 5, LVI). This is a fundamental right – which has been positivised through a rule of structure - which cannot be loosened by the impact of the principle of proportionality. The goal of this dissertation is to demonstrate that the principle of proportionality, on the fence of use of illegal evidences, overthrows the normative power of the Constitution, it converts the fundamental guarantee into an empty promise and unable to be fulfilled. The work also aims to demonstrate that the implementation of criminal justice depends on the inspection of the occurrence of facts which really support and make possible to apply the penal incriminating precept, but such verification activity is usually restricted in order to spare other values which are also protected by the constitution. This is a literature research which aims to show the main strands the above theme, which brings as a conclusion that the principle of proportionality is inapplicable when illegal evidences are found in any proceedings.