Cytomegalovirus infection is the first cause of viral congential infections. We studied the incidence of primary cytomegalovirus infection, searching for the presence of antibodies with an ELISA technique, in 939 pregnant women of a low socioeconomic level, attending a public outpatient clinic and 123 pregnant university students, attending a special outpatient clinic for students. The initially seronegative women were tested again during the second and third trimester of pregnancy to identify primary infections. The presence of cytomegalovirus congential infection in the newborns of infected mothers was investigated isolating the virus in cell cultures from urine samples. There was a higher prevalence of infection among low socioeconomic status women (95 vs 69.9%). Two women (one student and one coming from a low socioeconomic status) had a primary infection and in the newborn of the student, a congenital cytomegalovirus infection was detected. It is concluded that women's socioeconomic condition is not a risk factor for cytomegalovirus primary infection during pregnancy.