Purpose: To assess the impact of the mandatory adoption of the International Financial Reporting Standards (IFRS) on the quality of the financial information available on listed companies in the UK and France. Design/methodology: This research uses panel regressions to analyze the relationship between the idiosyncratic risk of stock returns and the opacity of financial reports, before and after the mandatory adoption of IFRS. Opacity calculations include different proxies of earnings management, according to the models used in the literature for the estimation of discretionary accruals, as a robustness test. Findings: Firm size influences the impact of IFRS in the UK, and the financial information of larger firms seems to have improved after IFRS adoption. In the case of France, the results do not support any improvement in the quality of the financial information after IFRS were put in place. Research limitations/implications: This research applies a new methodological approach to study the impact of IFRS adoption, but additional inquires on the subject are surely required. Practical implications: Certain features of the countries, such as the Common Law legal system and enforcement, could explain why the quality of the financial information for large firms has increased following the adoption of IFRS. It seems that the implementation of IFRS has given investors additional elements with which to ascertain a firm’s ability to generate future cash flows. Social implications: The adoption of IFRS, by itself, is not enough to improve the quality of financial information. Thus, regulators in countries adopting IFRS should consider additional reforms to ensure that the desired results are achieved. Originality/value: This work overcomes the methodological design problems of previous research, such as sample selection bias, the inclusion of observations close to the year of mandatory adoption, the heterogeneity of each country and the size of the analyzed companies. To the best of our knowledge, this research is the first to test the effect of IFRS adoption in the European context, using the relation between idiosyncratic risk and the opacity of financial reports.