A prospective study (1988 to 1990) to evaluate the risk of fetal cytomegalovirus transmission was conducted with 1771 pregnant women; the test results of 861 were seronegative (48.6%). At each prenatal visit they were tested for serologic data and cytomegalovirus excretion in urine, saliva, and cervical secretions. If seroconversion occurred (with or without cytomegalovirus excretion), ultrasonography, amniocentesis, and cordocentesis were performed at 22 weeks' gestation; 7 cases of primary cytomegalovirus infection were investigated. In 5 cases the amniotic fluid cultures were positive; in 3 cases the fetal blood test results were positive for specific immunoglobulin M; and in 2 cases brain ultrasonography results were positive. Infection was confirmed with biopsies of fetal tissue. In two other cases, the cord blood and amniotic fluid test results were negative, and the neonates were free of infection.