The analysis of the health risks associated with the administration of diethylstilbestrol (DES) during pregnancy (for the prevention or treatment of threatened abortions) has been largely published. Concerning mothers, a relationship between DES exposure during pregnancy and risk of cancer is unproved. However, existing studies are sufficient cause for serious concern over drug's carcinogenic potential, and further follow-up studies are required. Concerning daughters, a clear association between in utero exposure to DES and clear cell adenocarcinoma of the vagina or cervix is established (incidence between 0.14 and 1.4 per 1000 through age 24). The risk for squamous cell cancer of the vagina and cervix does not seem to be increased. Cervico-vaginal adenosis is frequent (20% to 60% of exposed subjects). This is not a pre-cancerous lesion, its spontaneous evolution is towards regression. No treatment is prescribed. Morphological changes of the genital tract have been described, their consequences on fertility and pregnancy are not clear. Concerning sons, an excess of genital abnormalities (especially of the epididymis and undescended testis) has been reported, but information on the fertility implications of these findings is not available. There is no evidence of an increased risk of testicular cancer. The analysis of all these informations should allow to bring up a policy to take into account these risks in the population.