Why does it always take a long time to acknowledge environmental hazards such as climate change or air pollution, even when knowledge on their dangers has been available for years? Drawing on the case of French pesticide regulation, this article shows that this gap between knowledge and consequent action results not only from secretive corporate leverage on public decisions and expertise but also from the expertise and bureaucratic machinery behind pesticide regulation. This machinery fosters an organized denial where regulators systematically exclude uncomfortable knowledge that could challenge official risk assessment. Organized denial that legally maintains ignorance fulfills an implicit function. It preserves the legitimacy of the risk management system and, through it, the administrative and commercial organization of agricultural production in France.