The primary objective of this project is to determine the prevalence and the ages when progressive and/or delayed onset of sensorineural hearing loss (SNHL) is most likely to occur in infants and young children due to congenital cytomegalovirus (CMV) infection. Our project is also defining risk factors in the newborn period that predict SNHL in CMV infected infants without clinically apparent disease. Our third aim defines the relative contribution of CMV infection to delayed onset hearing loss in the population. These aims are being achieved by identifying all newborns with congenital CMV infection from University Hospital and serially testing them to evaluate their hearing sensitivity at various ages. Also, a selected control group of newborns who are CMV negative ar being followed and compared to CMV positive children without hearing loss at birth. All infants born at University Hospital are currently screened virologically for congenital CMV infection by the investigators of this proposal. At 3 weeks, 3, 6, 9 and 12 months of age, each CMV positive infant has a complete audiological evaluation by a clinical audiologist that includes an auditory brainstem evoked response (ABR) and immittance measures for each ear. Also, each child has a complete audiological evaluation at 18, 24, and 30 months of age that includes behavioral audiometric assessment (visual reinforcement or play audiometry) and immittance measures to obtain pure tone thresholds, speech reception thresholds and speech discrimination score. The control group receives similar audiological evaluations at 3 weeks, 6, 12, 18 and 30 months of age. Currently we are continuing to enroll control children and collect information about possible risk factors that predict SNHL in CMV infected children. None of the controls have SNHL in the first or second year of life. About 8% of the newborns with congenital CMV have SNHL, with both progression and delayed onset of hearing loss documented in the first six months of life. Our proposal will provide better knowledge of the epidemiology and natural history of SNHL due to CMV. This information is essential for planning early detection and intervention strategies for SNHL in infants and young children.