BACKGROUND: Congenital toxoplasmosis may affect any organ, produce severe complications such as hydrocephalus and lead to ocular lesions which can appear late after birth. Fetal outcome can be fatal. During pregnancy, the mother can become infected, particularly by eating undercooked meat or poorly washed raw fruits and vegetables. In France, prevention of congenital toxoplasmosis is based on serial serology tests, performed repeatedly until delivery for pregnant women who remain negative then at the first prenatal visit. METHODS: We used toxoplasmosis serology data collected during national perinatal surveys conducted in 1995 and 2003 to estimate toxoplasmosis prevalence, assess risk factors and ascertain time trends in prevalence. In each survey, socioeconomic variables as well as the serological status for toxoplamosis were collected for all pregnant women who had terminated a pregnancy during a given week period. RESULTS: In 2003, 15,108 pregnant women were included; the prevalence of Toxoplasma infection was 43.8% (95% CI: 43.0-44.6). Prevalence increased with age and was greater for those who lived in the Southwest of France, the greater Paris area and in overseas districts. In 2003, as in 1995, prevalence increased with education level, occupational status of the household and number of pregnancies. Prevalence decreased 19% between 1995 and 2003. The decrease was significantly greater for pregnant women aged less than 30 years than for those aged more or equal to 30 years. CONCLUSION: Although it decreased over time, toxoplasmosis prevalence remained higher in France than in other European countries. With more than one out of two women in France susceptible of having Toxoplasma infection, it is important to promote preventive measures to avoid infection during pregnancy. (R.A.)