Applying institutional theory, we argue that environmentally legitimate firms incur less unsystematic stock market risk than illegitimate firms. Firms earn environmental legitimacy when their performance with respect to the natural environment conforms to stakeholders' expectations. This relationship was supported with the analysis of media reports and stock prices of 100 firms over a five-year period. The analysis also showed that firms with low environmental legitimacy can attenuate this effect by expressing commitment to the natural environment.