Realizing the potential of Embryo transfer (ET) for rapid, cheap and widespread dissemination of genetic material, the risk of transmission disease through the embryos must be considered. The aim of this paper is to evaluate theses risks at each step of production, storage and transfer. The pathogen agent may potentially originate from the donor male (semen) or the donor female (oocytes, embryos) and finally from the environmental conditions. As the differences between in vivo and in vitro derived embryos have been well described, evaluation of the potential risks should be assessed separately for in vivo and in vitro produced embryos. Even if this paper insist on the diseases or diseases agents that are more questionable, it clearly appears that ET remains the more safety way to transfer gene, provided prevention measures are properly handled (use of donor that are specific pathogen free, washing of embryos, additional treatment...) and furthermore it can be easily seen as the best way to prevent some disease transmissions (TSEs, leukosis, foot-and-mouth disease...).