This paper presents the research the goal of which was to gain an insight into teachers' opinions regarding the mistakes they make during classes and the ways to eliminate those mistakes. The sample comprises 300 primary school teachers and 115 vocational school and grammar school teachers in Serbia. Questionnaire with openended questions was used in the research. The first question required the group of teachers to state the example of one mistake they made during the class, and in the second question they were expected to state how they reacted in order to eliminate the aforementioned mistake. We classified the answers according to the following types of teachers' mistakes: didactic-methodical; expert-cognitive; personal; professional; pedagogical; social-moral. The findings of our research indicate that teachers perceive to a far greater extent the didactic-methodical than social-moral mistakes. It was shown that the greatest number of mistakes arises from the wrong decisions or insufficiently thoughtful decisions of teachers. We also analyzed the ways in which teachers try to eliminate their mistakes.