On the 1st of May 2004, Poland became a member state of the European Union. At the moment, it doesn’t fulfill the convergence criteria required for the introduction of the euro, but will have to adapt in the future. The aim of this article is to identify potential risks and economic costs that could occur due to Poland's integration with the eurozone. The joining country loses the ability to run an autonomous monetary policy. The scale of adverse effects depends, among other factors, on decisions made by the European Central Bank, effectiveness of adjustment mechanisms and types of shocks. Economic costs may occur on a long time scale, which is related to the fact that economic structure of Polish economy is not exactly similar to the EU and there is low flexibility of wages in Poland. Most countries of the eurozone do not fulfill the fiscal criteria, creating a threat to the economy. The article sums up possible consequences of introducing the single currency that are expected and should be taken into consideration before joining the eurozone.