This research examines sustainability assurance practices and more specifically whether media pressure influences companies’ decision to implement a voluntary sustainability assurance. The sample consists of companies listed on the French SBF 120 over a period of four years (2007–2010). The study conducts logistic regressions with longitudinal panel data to empirically test the influence of explanatory factors on the use of sustainability assurance. It appears that the variables related to media pressure explain the establishment of sustainability assurance. Moreover, the size of the company, the industry and the positioning of companies in corporate social responsibility also influence the use of assurance of sustainability information. On the theoretical level, the research contributes to a better understanding of practices of sustainability assurance by offering an explanatory model of this practice. On a managerial level, it contributes to the understanding of corporate behavior. This research may allow users of sustainability information to judge the relevance of sustainability reporting.