The article discusses the problem of demanding the opinion on the state of the psychic health of the defendant and its influence on the course of criminal proceedings. The Author presents the core of the condition of the state of justified doubt from the point of view of demanding the opinion establishing the sanity of the defendant at the moment of the commission of the forbidden act as well as on his present state of mental health and especially referring to the issue whether that state makes it possible for the defendant to participate in the proceedings and to conduct his defence on his own. Then the Author discusses the meaning and the importance of the decision of a procedural body referring to the admission of evidence in the form of a court psychiatric opinion, its influence on the further course of the proceedings and the legal consequences of not asking for such an opinion.