Abstract It was widely anticipated before European Union enlargement that the accession states would have a negative impact on EU environmental governance. By extension, the European Parliament's (EP) reputation as an environmental champion might be threatened by the influx of MEPs from accession states. An analysis of all EP amendments to environmental legislation between 1999 and 2009 reveals that post-enlargement the EP was more successful at securing the adoption of its amendments into law but that these amendments were less radical. These changes arise from the institutional adaptation prompted by enlargement and a broad ideological shift to the right within the EP.