Since the 1940s, diaethylstilbestrol (DES) has been used by millions of pregnant women to prevent miscarriages and many other disorders in pregnancy. In 1971, it became clear that this apparently innocent treatment proved to be a time bomb for the infants exposed to DES during the first trimester of pregnancy. DES is now associated with an increased risk of breast cancer, clear cell adenocarcinoma (CCAC) of the vagina and cervix, and reproductive anomalies. This article summarises the potential long-term health implications of DES on the mother, DES daughters and DES sons, and the possible side effects on the third generation. Health care professionals have to know the history of DES to prevent future disasters with drugs prescribed.