Congenital toxoplasmosis results from contamination of the foetus by Toxoplasma gondii during pregnancy. It is a frequent and severe condition calling for close surveillance of mothers at risk. During the last few years, numerous advances have been made in the diagnosis and treatment of toxoplasmosis. Its diagnosis in the mother is now more reliable due to improvements in serological techniques, while in the foetus the use of foetal vascular techniques has made it possible to detect those who are infected. Owing to a new and effective therapeutic method certain foetuses can now be treated successfully in utero, so that induced abortion is reserved to cases with severe and early toxoplasmosis. The contribution of new molecular biology techniques to advances in this ever moving field is explained.