The impact of the EU law on patients' rights in cross-border health care on national health care systems was subject to many fervent debates among European academics. For all the rhetoric of that debate, beneath it lies an attempt to delimit the boundaries of EU competences. These were determined by the Court’s interpretation of the Treaties. However, the recent development of patients' rights has escaped the boundaries of this interpretation and broadened the influence of patients' free movement rights into social fields. The primary concern is to answer the question about the cause which brought the Member States to give up their sovereignty for the sake of the internal market and about the effects of these sacrifices for the EU, the States and European citizens respectively. The detailed analysis of the development of EU law on cross-border health care proves that this system was an inescapable result of the decisions taken decades ago. Furthermore, by examining the different definitions and meanings of the European Social Model, the argument is explored that EU law on patients' rights, in its present form, can be considered to be not only a factor enriching the European Social Model but also an actual part of it. A new type of solidarity among the Member States and the citizens of the European Union exists, namely functional solidarity. The subject of cross-border health care has been analysed by academics in all possible ways. However, the points of view of the countries that only recently joined the Union are different to the points of view of the states that participated in the creation of the cross-border health care system. The aim of this thesis is to contribute to the debate by placing focus on the fact that there is a very important difference between the effects caused by the development of the cross-border health care systems in "Old” and "New” Member States. The thesis will describe the impact of EU law on cross-border health care in the national systems and the opposition raised against it. The objective of this work is specific. It aims to underline the difference in the impact of cross-border health care on "Old” and "New” Member States, as well as the different interests of these two groups of states in relation to EU health care policy. The intention is not only to give an empirical impression of the impact of European integration on the set-up of healthcare states, but also to explore the different tensions caused by the cross-border health care system and the different expectations of it. An attempt will be made to prove that the relation between the EU law and the national health care systems was built on two-way influence. Not only did the Member States alter their health care systems to accommodate the rules of the internal market, but that the system of co-ordination of social security also had to be adapted in order to fit the multiple national systems.