Significant decreases in both male and female fertility have been observed over the past 50 years, with female conceptions rates dropping by 44% and male sperm counts decreasing by over 50%. This dramatic decrease in fertility can be attributed in part to our increasing exposure to endocrine disrupting chemicals (EDC’s). Diethylstilbesterol is an estrogenic EDC that was prescribed to millions of pregnant women between 1940-1970 and resulted in detrimental reproductive effects in the offspring that were exposed in utero. Women who were exposed to DES in utero experienced higher rates of infertility, pregnancy complications and reproductive cancers. Alarmingly, there is evidence to suggest that these effects may persist in the grandchildren and great grandchildren of exposed women. To determine if exposure to DES can result in transgenerational impacts mice were exposed to 100ug/kg of DES every second day from days 9-17 of gestation as this period of fetal sexual differentiation and development is particularly vulnerable to EDCs. The effects of DES were monitored in the F1-F4 female descendants. Pregnancy rates for F1, F2 and F3 DES females were reduced compared the controls and the fertility index also decreased in the F1, F2 and F3 generations. The onset of puberty was also affected in these females, with the vagina opening significantly earlier in the F1, F2 and F4 females compared with controls. These results indicate a transgenerational effect of DES on fertility and timing of puberty. This has implications for the 50 million DES descendants as well as raising health concerns for the ongoing health impacts caused by exposures to other estrogenic EDCs which are pervasive in our environment.