When we examine the thesauri prepared in the framework of college or university dissertations, we can draw important lessons. The outcomes reveal not only all the common mistakes that are characteristic of LIS students' dissertation works, but also the shortcomings of the teaching of the subject at LIS schools. In these dissertations, Hungarian library standards are sometimes ignored, while problems can be observed in the distinction of conceptual and linguistic levels as well as in interpreting generic relations. The teaching of thesauri cannot be separated from the teaching of the MARC21 and HUNMARC data exchange formats for authority data. LIS students should get thorough and exhaustive training in this field, especially because they will work with these formats on.