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Several million women were treated and their fetuses exposed to diethylstilbestrol from the early 1940s to the end of the 1970s, when we did not have medical knowledge of the long-term consequences of fetal exposure to various therapies, or underestimated these consequences. The adverse effects of exposure to diethylstilbestrol on prenatally exposed women and men are widely documented, dominated by adverse pregnancy outcomes in women, and the increased risk of cancer in exposed children of both sexes. There is no longer any doubt that diethylstilbestrol acts as an endocrine disruptor with consequences for the offspring of those exposed, including the grandchildren of women who were prescribed diethylstilbestrol during their pregnancy. Several links in the chain that could have stopped prescription failed, in defiance of the precautionary principle. The history of diethylstilbestrol must therefore be taught in various ways. It serves as a model for thinking about the trend in the medical world to have great enthusiasm for a product or a new technology, but for which, because of the means we now have at our disposal, we absolutely must ensure both efficacy and safety. Faced with the continuing and undeniable progress in the field of reproductive medicine, we must remain vigilant, in particular when it comes to all hormonal therapy prescribed in the early stages of fetal development.