Diethylstilbestrol (DES) has been identified in the early 1990s as the first endocrine disruptor, from which the long-term effects of many chemicals on human reproductive capacity can be expected. Yet, the DES French history is one of forgetfulness, neglect and refusal of learning that were repeated until the early 2010s. On the basis of a qualitative sociological research, this article sheds light on the different mechanisms in the production of ignorance that made DES a failed precedent. We identified three complementary processes to understanding the marginalization of this issue: lack of identification of exposed populations, low accumulation and dissemination of knowledge, long-term isolation.