We consider the impact of the 2004 EU enlargement on enterprise performance and the exporting behavior of German service enterprises in Germany's eastern border region. Our results from regression adjusted difference-in-differences estimators combined with matching and panel data from official statistics suggest that the EU enlargement had a negative impact on the turnover and export intensity of large enterprises in the border region. For small enterprises, we find an annual increase in turnover by 2.3% in 2004 and an annual decrease in profitability by 1.5 and 1.9 percentage points in 2004 and 2005, respectively.