From 1941, the synthetic oestrogen diethylstilbestrol (DES) was administered to millions of women around the world to prevent miscarriages. In 1971, a clear and direct link was shown between taking DES during pregnancy and its subsequent long-term morbid effects on offspring. In the last 50 years, the list of side effects of in-utero exposure to DES has grown to include cancer, infertility, significant prematurity and urogenital malformation, amongst others. Based on qualitative sociological research conducted between 2010 and 2013, compiling archives, judicial documents and 108 interviews, this article illustrates a continuous production of ignorance in France. By focusing on DES as a reproductive health technology, three aspects are stressed. First, in terms of recognition of adverse effects, despite DES being identified as a prototype for other technologies such as the contraceptive pill or hormone replacement therapy, there remained a strong reluctance to import knowledge from the USA on its dangers and risks. Second, there was indifference to transgenerational side effects: even when the most visible effects of DES were finally acknowledged, there was a lack of consideration of the health of descendants; an inability to deem the knowledge of these repercussions as emancipatory or potentially empowering for the offspring. Third, regarding the health care of DES daughters, an important propensity to undone science is highlighted, with notable indifference to the risks of hormonalization of the female body, even on the part of activists. Thus, decades after it was last given to pregnant women, the shadow of DES still lingers as a failed reproductive health technology. © 2021 The Authors