Eighty-nine cases of proven Toxoplasma gondii fetal infection were studied in order to describe the morphological lesions which could be demonstrated on ultrasound examination; these were present in 32 of the infected cases. Cerebral ventricular dilatation was the most common sign and was generally bilateral and symmetrical. Its evolution was always very rapid over a period of a few days. Other signs observed included intracranial and intrahepatic densities, increased thickness and hyperdensity of the placenta, ascites and rarely pericardial and pleural effusions. Thirteen fetuses demonstrated two or more ultrasound features. Intrauterine growth retardation and microcephaly were not observed. Ultrasonographic assessment of the fetus injected with Toxoplasma gondii is important. It improves the reliability of prenatal diagnosis and is of important prognostic value in cases with severe brain lesions, but is of little value in detecting brain necrosis without ventricular dilatation.