Abstract: What was the effect of the 2004 and 2007 EU enlargement on the emission intensities in new and old member states? In this study we analyse a multidimensional panel with data on almost all EU member states from 1995 to 2015. We estimate the effects on the manufacturing sector level on carbon dioxide (CO2), sulphur oxide (SOx) and nitrogen oxide (NOx) emission intensities. While we find little direct effect of the individual enlargement steps, we find some support for both the Pollution Haven Hypothesis and the Factor Endowment Hypothesis, which are both based on increased intra-EU trade integration. This result also provides support for potential within-Europe carbon leakage channels. Additionally, we can establish that income growth, spurred by the accession, might have lead to decreases in emission intensities by several tens of percent within manufacturing sectors. This latter finding presents an optimistic outlook for future accession countries.