Purpose – The purpose of this paper is to assess to what extent the loss of the ISO 9001 certification affects the decertified firms’ financial performance. Design/methodology/approach – Using standard event study methods, this paper matches a sample of 143 Portuguese companies that lost their ISO 9001 certification with similar non-event counterpart firms (according to return-on-assets (ROA) and size) and compares the performance of these two groups of firms using financial data collected from the AMADEUS database. Findings – Results show no statistical significant differences in the financial performance (as measured by ROA, return-on-sales (ROS) and sales growth) between companies that lost their ISO 9001 certification and their matched firms. Although the literature suggests that certification improves firms’ performance and that the benefits of certification may last over long periods of time, this paper’s results suggest that, after decertification, companies do not exhibit over or underperformance in their operations vis-à-vis comparable firms that do not undergo the same event. Originality/value – As far as the authors are aware, this is the first study assessing the impact of ISO 9001 certificate withdrawal on the decertified firms’ financial performance.