Cervical cultures for cytomegalovirus (CMV) and samples of blood for antibody to CMV were obtained from 1,129 pregnant women: 57% of the women had antibody to CMV, and 14% of seropositive women shed virus. Logistic regression analysis showed that seropositivity correlated with lower socioeconomic status, birth outside North America, multigravidity, older age, history of abnormal cervical cytology, infection with Trichomonas vaginalis, a first pregnancy at less than or equal to 15 years of age, and greater total numbers of sex partners. Thus, past exposure to CMV relates both to sociocultural factors and to sexual behavior. Absence of such risk factors identifies women who are at highest risk for primary infection with CMV during pregnancy. Culture positivity in seropositive women was independently associated with younger age, later stages of pregnancy, and race. Among seropositive women less than or equal to 21 years of age, 35% shed CMV in the third trimester, a finding of epidemiological importance with regard to perinatal transmission.