To identify maternal risk factors for intrauterine transmission of cytomegalovirus (CMV), a case-control study of 175 mothers of neonates with congenital CMV infection was undertaken. Cases and 358 randomly selected controls delivered neonates between 1980 and 1988; in this interval neonates were routinely tested for viruria. Eighty-four percent of the study population was black and >87% received prenatal care. Women with gonorrhea, trichomoniasis, or bacterial vaginosis had an increased risk of intrauterine transmission of CMV, as did those who were primigravid (odds ratios, 1.8-2.5). Women who were young, unmarried, and of lower income were almost four times more likely to deliver a CMV-infected newborn than were those who did not have all three of these factors. These results in a predominantly black, low-income population indicate a greater risk for congenital CMV infection in offspring of young, single, primigravid mothers. The association with gonorrhea and other sexually transmitted infections suggests that sexual activity is an important source of maternal CMV infections that result in congenital infection in this population.