On account of the geographical closeness, relations between Poland and Sweden have abounded over centuries with significant events not only in the area of politics but also in economy and culture. The near vicinity also contributed to the outbreak of a military conflict between the states in the 17th century. The wars from a long gone past have little impact on the present-day relations between Poland and its northern neighbour. In Sweden hardly anyone remembers about them. This publication analyses the impact of the membership of Poland and Sweden in the same integrating grouping – the European Union – on their bilateral relations. To prove the thesis and research questions it was necessary to analyse the whole range of relations between the two states over a long time horizon. Thus, the post-war Polish-Swedish relations were divided into three stages. The first one covers the period when the two analysed states were out of the European integrating structures. The second stage covers the years of 1995-2004, when Sweden already was a member of the European Union and Poland aspired to be one. The last stage is the initial period of common membership in the EU.