Existing high levels of temporary migration between Central and Eastern Europe and the European Union (EU) have highlighted a number of concerns relating to the eastern enlargement of the Union. While much of the debate has focused on the destinations, we use Slovakia as a case study to explore economic implications for the countries of origin of highly skilled migrants. First, the paper examines estimates of the scale of “youth brain migration”, comparing survey-based and expert-opinion estimates with our own estimate based on reconciling labour market and educational data. This identifies a substantial loss of graduate workers from the labour force through migration, accounting for a potentially significant proportion of Gross Domestic Product (GDP) growth. Second, we consider whether such migration will constitute “brain drain/overflow” or “brain circulation”: in other words will it be temporary or permanent? In some ways, however, this is a false dichotomy, for there are strong links between initial temporary migration and intended permanent migration, explored here through a survey of the motivations and social networks of returned migrants. Third, we address the ability of national states to intervene to mediate such losses. We generally concur with other commentators on the need for a multi-scalar and multi-functional approach, focusing especially on economic development. However, we are pessimistic about the likely speed of economic convergence and, moreover, argue that initial temporary migration (with implications for permanent migration) will continue to be driven by non-economic goals.