The purpose of this paper is to analyse to what extent accession to the European Union affected the quality of institutions in Romania and Bulgaria. In order to measure these effects, indicators of perceived corruption have been built based on data from the Life in Transition surveys I, II, III, conducted by the European Bank of Reconstruction and Development. Under the specifications of a difference-in-differences methodology, evidence of a reduction in small acts of corruption has been discovered for both countries, with larger effects in Bulgaria. In regards to high level corruption, Romania proved to be successful in tackling this dimension nine years after the accession, while for Bulgaria the evidence suggests an unfavourable deterioration over time.