This investigation consisted of a longitudinal study of the effects of congenital cytomegalovirus (CMV) infection on hearing sensitivity in 860 children with documented asymptomatic or symptomatic congenital CMV infection. Of the 651 children with asymptomatic CMV infection, 48 (7.4%) developed sensorineural hearing loss (SNHL), compared to 85 (40.7%) of the children with symptomatic CMV infection. Children in both groups experienced latent effects consisting of delayed onset of loss, threshold fluctuations, and/or progressive loss of hearing. It can be concluded that congenital CMV infection is a leading cause of SNHL in children. The late onset and progression of loss necessitates continued monitoring of hearing sensitivity in this population.