The Lisbon Treaty from 2009 introduced the possibility for individual member states to withdraw from the European Union (EU) on the basis of a unilateral decision. In June 2016 the UK decided to leave the EU invoking article 50 of the treaty. But is withdrawal democratically legitimate? In fact, the all affected principle suggests that it is undemocratic for subunits to leave larger political units when it adversely affects other citizens without including them in the decision. However, it is unclear what the currency of this affectedness is and, hence, why withdrawal would be undemocratic. We argue that it is the effect of withdrawal on the status of citizens as free and equal that is decisive and that explains why unilateral withdrawal of subunits from larger units is democratically illegitimate. Moreover, on the ‘all affected status principle’ that we develop, even multilaterally agreed withdrawal is undemocratic because the latter diminishes the future ability of citizens to make decisions together regarding issues that affect their status as free and equal. On this basis, we conclude that it is undemocratic for a member state such as the UK to withdraw from the European Union.