The aim of this study was to determine the sero-prevalence of cytomegalovirus (CMV) IgG antibody in pregnant women in Ireland and assess individual risk factors for prior acquisition of CMV. In 2002, sera from 1047 pregnant women were tested by enzyme immunoassay for CMV IgG. Age and nationality were recorded for each patient. Among Irish-born women the following additional factors were also recorded: socio-economic status, number of children and occupational exposure to children. Only 30.4% (204/670) of Irish women were CMV antibody positive compared to 89.7% (322/359) of non-Irish women (p < 0.001). Non-Irish women were mostly from Sub-Saharan Africa, Eastern Europe and Asia. Lower socio-economic group and increasing number of children were significant independent predictors of CMV sero-positivity among Irish pregnant women (p < 0.05). Irish pregnant women have one of the lowest reported CMV sero-prevalence rates worldwide, indicating low circulation of CMV within the community. However, up to 70% of Irish women are susceptible to a primary infection during pregnancy.