With a reported prevalence of 7 per 1000 births, congenital cytomegalovirus (cCMV) is a frequent condition. In addition to the risk for neurodevelopmental disabilities, it is the major cause of congenital nonhereditary sensorineural hearing loss in developed countries. Hearing loss can be unilateral or bilateral and the extent varies from mild to profound. It may be present at birth or develop within the following years. Progressive and fluctuating hearing thresholds make diagnosis challenging. Current literature shows large variability in prevalence and presentation, so more long-term studies are required to describe the nature of the hearing loss. Since 2007, a multicenter Flemish CMV register collects data from children with cCMV in a prospective way. The first objective is to extensively describe the audiological follow-up until the age of 6 years in a large group of cCMV patients. The correlation of hearing phenotype with viral load and timing of seroconversion will be innovative. Systemic valganciclovir is the gold standard for symptomatic cCMV patients, although its impact on hearing remains contradictory. For our second objective, we will perform an explanatory research to estimate the effect of (val)ganciclovir on hearing outcome. The third purpose is to investigate the effect of local therapy in a mouse model, in order to avoid the current systemic side-effects. With this research project, we aim to provide a more suitable approach for cCMV associated hearing loss