Many congenital infections can produce foetal diseases and are sometimes responsible for major disablements. The most frequent infectious foetal diseases are toxoplasmosis, rubella and chickenpox. Diseases caused by parvovirus or cytomegalovirus are exceptional. Foetal blood sampling has considerably simplified the prenatal diagnosis and made it accessible to more medical centres; it has also widened the therapeutic possibilities and above all, it has considerably reduced the number of therapeutic abortions. It may well be that the development of molecular biology, which has the great advantage of permitting an earlier diagnosis, will in the near future make it possible not only to detect numerous monogenic diseases before birth, but also to diagnose some foetal infections. We might then hope that a much earlier treatment in utero will also be more effective.