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The etiology of sensorineural hearing loss (SNHL) in children may be viral. This cross-sectional study aimed to determine the role of viral infectious agents in children with idiopathic SNHL. Of 119 children with SNHL aged 3-168 months undergoing cochlear implant surgery at a hospital in Tehran, no cause could be established in 18 cases (15.1%). Cytomegalovirus (CMV) and herpes simplex virus (HSV) active infections (detected by DNA-PCR, confirmed by serology) were found in the perilymphatic fluid of 16.7% (3/18) cases of idiopathic SNHL. Serology was performed on blood samples from 11 of these cases: specific antibodies against CMV, Toxoplasma spp., HSV and rubella were determined in all cases; acute T. gondii infection was detected in 7 cases and rubella IgG was found in only 1 case. Neonatal screening for CMV, HSV and T. gondii may be helpful in the Islamic Republic of Iran.