The development of the EU citizenship concept within the current boundaries of the Union is incompatible with some of the terms of enlargement, namely the policy of transition periods, outlined in the Act of Accession. While the ECJ has tried to interpret EU citizenship as a ‘fundamental status’, the 2003 Act of Accession introduces limitations on the freedom of movement – a core citizenship right – thus undermining the European citizenship concept and the idea of equality for all Europeans. Unfortunately, this situation is made possible by the wording of Article 18 EC itself, which allows for conditions, thus opening the door for the creation of ‘second class’ citizens. This paper argues that the most recent enlargement offered an opportunity to bring about a new understanding of equality at the European level and give real meaning to the European citizenship concept, completing rather than undermining the achievements of the ECJ, and taking into account the lessons of previous enlargements. In light of this, the Articles of Accession represent a missed opportunity.