Objectives:
The purpose of this study is to draw attention to an important procedural institution, which is the prohibition of changing the decision to the detriment of the appellant. This prohibition is an important civilization achievement in every legal procedure, including administrative proceedings. The study presents the legal regulations of this interdict in administrative proceedings of Central European and Balkan countries. The choice of these countries is not accidental: the laws of the Austro-Hungarian monarchy had in the past codified the administrative proceedings of these countries and then deeply influenced them.

Material and methods:
The article uses the normative acts of these countries as well as the views of the doctrine and judicial decisions. First of all, the focus was on the views of doctrine.

Results:
In some of these countries it is believed that reformatio in peius is a natural consequence of lodging an appeal and there is no need to limit it. At the same time, in other countries the restriction of reformatio in peius seems justified, and the legislator introduces broader or narrower prohibitions on changing the decision to the detriment of the appellant party.

Conclusions:
The pioneers in the consistent protection of the appealing party against the possibility of deterioration of the legal situation were: the Polish APA of 1960 by the prohibition of reformationis in peius, and the law passed in the former Yugoslavia in 1957. The prevailing view is that the prohibition of reformationis in peius is an important procedural guarantee for a party to the proceedings. Its validity is justified by reference to the basic principles of this procedure, such as the principle of protection of a party's interests and the principle of protection of their trust in state bodies.