We examine the effects of a proposed border adjustment tax on the share prices of publicly traded firms. Border adjustment refers to exempting export revenue from taxation while also disallowing deductions for the cost of imports, and has been proposed as a potential U.S. corporate tax reform. The economic effects of the border adjustment tax have proved to be highly controversial, with wide differences of opinion among experts, but little in the way of empirical evidence. To provide empirical evidence on the shareholder wealth effects of border adjustment, we examine equity market reactions on days with high attention paid to the proposed border adjustment tax. We develop a daily index of attention to the border adjustment tax using internet search volume as reflected in Google Trends. We find evidence of significant shareholder wealth effects from the proposed border adjustment tax. Specifically, firms in retail and other import-intensive industries experience significant, negative stock returns on days of high attention to the border adjustment tax. This response is mitigated in firms with foreign operations.