The diagnostic problems linked to human cytomegalovirus (HCMV) in pregnancy are many and not all have been fully defined. In long-term seropositive women there is a tacit agreement that no laboratory testing for HCMV should be carried out. In seronegative women a test for HCMV-specific IgG should be performed at least twice during the first 4 months of pregnancy, and if the seronegativity persists, further follow-up might be stopped. On the other hand, if a seropositivity appears the diagnosis of a primary HCMV infection is established and prenatal diagnosis should be offered to the mother. Finally, in the case of a pregnant woman with unknown serological status, the diagnosis of HCMV infection is a complex problem and several different questions need to be addressed. In our opinion they should be screened with a reliable IgM test (confirmed by blot if necessary) followed, in the case of positivity, by an avidity assay. Pregnant women undergoing a primary HCMV infection should be encouraged to seek prenatal diagnosis to be performed by PCR and virus isolation from amniotic fluid at the 21st to 23rd week of gestation.