This paper aims to advance in the knowledge of the economic impacts of ISO 50001 certification on firms' performance. Our main research hypothesis is that ISO 50001 is associated with improvements in market value of firms. To test this hypothesis, we employ an event study methodology for a sample of 120 companies listed on different stock exchanges, and use market reaction to the announcement of ISO 50001 as a proxy for changes in firm performance. We reveal that market reaction to the adoption of ISO 50001 is negative but statistically insignificant. This result is not suggesting that getting ISO 50001 is a bad investment, but rather that inflated expectations of financial performance improvement due to the adoption of ISO 50001 are still unfounded. © 2014 Elsevier B.V.