Congenital toxoplasmosis is a risk for fetus both in 'low' and 'high risk' areas. A cost-benefit analysis based on data from a Finnish prospective study (20.3% seropositivity of pregnant mothers and incidence of 2.4/1,000 seronegative pregnancies) and on Finnish cost data was performed to compare the no-screening and screening alternatives for primary toxoplasma infections during pregnancy. A maternal-feto transmission risk of 40%, effectiveness of treatment of 50%, and discount rate of 4% were used as other baseline probabilities. The calculations were carried out by decision analysis combined with sensitivity analysis. The total annual costs of congenital toxoplasmosis without screening amount to US$ 128/pregnancy/year, and with systematic serological screening, US$ 95/pregnancy. Thus screening reduces the costs by 25%. The present value of net savings in Finland would be US$ 2.1 million every year. A one-way sensitivity analysis showed that screening together with health education is preferable to health education without screening if the incidence of maternal primary infections exceeds 1.1/1,000 and effectiveness of treatment is better than 22.1%. Screening for toxoplasma infections during pregnancy is economically worthwhile even in a country with a low incidence. A scheme of systematic screening for maternal primary toxoplasma infections combined with health education should be considered.