Several studies have found a relationship between corporate social and environmental disclosure and firm value (FV) or accounting profitability. Where environmental disclosure has been the focus, though, only single-country studies have been published, and most of the previous research concerns the developed world. This study examines the association between corporate environmental disclosure (CED) and FV in the Gulf Cooperation Council (GCC) countries, where CED has been increasing from its previous low base. Findings from a multicountry sample of 500 firm-year observations using a 55-item unweighted environmental disclosure index suggest that CED is significantly and positively related to FV as measured by Tobin's Q (TBQ). The relationship is robust to using a weighted version of the disclosure index, individual countries and environmental disclosure subindices. Some evidence of a positive relationship between CED and return on assets is also found, but even where statistically significant, the relationship is much weaker than in the case of TBQ. For empirical and theoretical reasons, we recommend that future studies pay greater attention to market-based proxies, if possible, when investigating the value relevance of CED in both developed and developing countries. Our results suggest that both managers and policymakers in GCC countries should take a positive view of expanded CED.