In September 2013, the Polish Parliament passed an amendment to the Code of Criminal Procedure. The legislators decided to expand a number of adversarial elements present in current Polish criminal proceedings. When these changes come into effect (July 1, 2015), Polish criminal procedure will be similar to American regulations, in which the judge’s role is to be an impartial arbitrator, not an investigator. The authors of the article describe the meaning of the principle of adversarial trial in Poland. They also emphasized relations between this principle and the concept of “material truth”. The changes established by the amendment are shown in perspective of the American definition of adversarial trial. The authors analyze the reform and attempt to predict the problems with new regulations in practice.