In this longitudinal study of cytomegalovirus in 4578 pregnant women of middle/upper socioeconomic status in Houston, 52% had cytomegalovirus antibody when enrolled, and 48% were serologically susceptible. Studies were completed on 3899 mothers and their infants; 2.2% of these women experienced primary cytomegalovirus during pregnancy and 24% of those with primary infection transmitted cytomegalovirus to their infants. Of 22 cytomegalovirus-infected infants, 2 had disease at birth and 20 were asymptomatic. One symptomatic infant (primary maternal infection) has developmental delay. The other (immunocompromised mother with cytomegalovirus antibody before pregnancy) had hepatitis but has no symptoms at 1 year of age. On follow-up, 4 of 16 infants asymptomatic at birth have sequelae (hearing loss in 3, developmental delay in 1). All four were born to mothers with primary cytomegalovirus infection. Infant outcome was not related to trimester of maternal infection.