The paper discusses the situation of a Polish corporation transferring its register office abroad. The Polish Commercial Companies Code provides that in order to transfer of the corporation's registered seat abroad it is necessary to adopt a resolution by the general meeting of shareholders and thereafter carry out the liquidation and dissolution of the corporation. As result, the Polish law prohibits the cross-border conversion, i.e. the transfer of the registered seat abroad with a change of the national rules that apply to the statue of the corporation. This situation is incompatible with the EU freedom of establishment. The European Court of Justice stated in the Cartesio judgement on 16 December 2008 (C-210/06) that the Member State of company's register seat may not prohibit the company from transferring its seat to another Member State, as long as it is connected with converting itself into a company governed by the law of another Member State. In addition, the prohibition of cross-border conversion in the Polish law is not fully justified by the protection of the company's stakeholders. Under current law, there are measures that adequately protect the interests of creditors, employees, minority shareholders and the fiscal interest of the state. As a result, there is an urgent need to change the Polish law in order to enable Polish corporations to transfer their register seat to another EU member state.