The UK's decision to leave the EU is surrounded by several studies simulating its potential effects. Alternatively, we examine expectations embodied in stock returns using a two-part estimation process. While most firms' prices fell, there was considerable heterogeneity in their relative changes. We show that this heterogeneity can be explained by the firm's global value chain, with heavily European firms doing relatively worse. For firms with few imported intermediates, this was partially offset by a greater Sterling depreciation. These changes were primarily in the first two days and highly persistent. Understanding these movements gives a better understanding Brexit's potential effects.1 Norway has a free trade agreement with the EU but is not a member of the EU's customs union, so it faces the non-tariff barriers that apply to non-EU countries.2 Other studies in this vein, which cover various simulation exercises, include Head and Mayer (2015), PWC (2016), Fraser of Allander (2016) (who focus on Scotland), HM Treasury (2016),and OECD (2016). All of these find negative effects of various magnitudes whereas Minford, et al. (2016) finds the potential for positive impacts on the UK. It should be noted that Sampson, et al. (2016) argue that Minford, et al.'s optimism is based on implausible assumptions on trade barrier changes and import elasticities.3 Head and Mayer (2015) describe three possible disadvantages of Brexit for FDI. First, an increase in trade barriers makes production in the UK less attractive because it becomes more costly to ship to the rest of Europe. Second, supplying inputs and staff from brands headquarters becomes more difficult (higher co-ordination costs). Third, UK products become less attractive to EU consumer after Brexit.4 Strictly speaking, this is a return that is 14.4% worse than expectations; since in the long run a firm's return should equal the market, results in our comparison. See below for a detailed discussion of how to 11 Timmer, et al. (2014b) provide a recent overview of this literature. 12 Davies, et al. (forthcoming) find that tariff pass-through within a multinational is roughly half that of an arm's length transaction.13 See London Stock Exchange (2010) for details.