The adversarial principle can be considered as one of the indispensable principles of not only criminal proceedings but also proceedings integrated in other branches of national law of the Slovak Republic. So it is appropriate to recognize its important position and emphasize that its omission may have far-reaching consequences. Its importance underline also wide range sources of law. In practice, focusing primarily on criminal law, we encounter with its limitations, particularly from the perspective of the accused person in the ongoing criminal proceedings, especially by examination of witness whose identity must remain classified. The main aim of the article is to point out how the right of an accused person on adversarial examination of witness whose identity must remain classified can be guaranteed through the conditions which declares European Court of Human rights and which are required for the applicability a testimony of this witness as an evidence in criminal proceedings.