Background Toxoplasma gondii is one of the world’s most common parasites. Primary infection of the mother during pregnancy can lead to transmission to the fetus with risks of brain and eye lesions, which may cause lifelong disabilities. France instituted a national program based on monthly retesting of susceptible pregnant women to reduce the number of severe cases through prompt antenatal and postnatal treatment and follow-up. Objective To evaluate the ability of the French prenatal retesting program to reduce the lifetime costs of congenital toxoplasmosis. Methods We measured and then compared the costs and benefits of screening vs. not screening using decision-tree modelling. It included direct and indirect costs to society of treatment and care, and the lifetime lost earnings of children and caregivers. A probabilistic sensitivity analysis was carried out. Findings Total lifetime costs per live born child identified as congenitally infected were estimated to be €444 for those identified through prenatal screening vs €656 for those who were not screened. Estimates were robust to changes in all costs of diagnosis, treatment, and sequelae. Interpretation Screening for the prevention of the congenital T . gondii infection in France is cost saving at €212 per birth. Compared with no screening, screening every pregnant woman in France for toxoplasmosis in 2020 would have saved the country €148 million in addition to reducing or eliminating the devastating physical and emotional suffering caused by T . gondii . Our findings reinforce the conclusions of other decision-analytic modelling of prenatal toxoplasmosis screening.