A great number of works that deal with party systems of the Central and Eastern European countries focus on communist successor parties. This paper aims to illuminate some causes of different development of identity of the communist successor parties in Poland, Hungary, the Czech Republic and in Slovakia. The paper identifies as the main causes above all 1) readiness of a segment of the communist party leadership, i.e. the party reformists, to change the party orientation in direction of social democracy and 2) willingness of some party members to give support to such a change. Also, time played an important role in the process in that a new party outlook had to be adopted as soon as the former political system collapsed. The ex-communists in Hungary, and in Poland serve examples of successful identity transformation, which lead to early return to the government. As far as the Czech Republic is concerned, absence of a reform wing in the Communist Party before 1989 and a lack of willingness of the majority of its members who remained in the party after the system collapsed lead to preservation of the orthodox identity of the successor party (the Communist Party of Bohemia and Moravia - KSČM). Although in Slovakia the Communist Party has shifted towards social democratic principles, the whole process occurred relatively later on. The rise of the successor Party of the Democratic Left (SDL) encountered an expansion of the Movement for a Democratic Slovakia (HZDS). HZDS managed to take over a great part of the potential voters who would vote for the ex-communists, which put the Party of the Democratic Left into the position of a less significant subject in the Slovak party system. The final part of the paper deals with some circumstances that had impact on the success, unique in Central and Eastern Europe, of the historical Czech Social Democrats.