We encountered 2 patients with bilateral hearing loss due to the mumps virus in one and the varicella-zoster virus in the other. Each virus was identified by a serological test, and virus-specific IgG and IgM antibodies were detected in the sera. In both patients, hearing loss on the contralateral side occurred a few days after that on the initially affected side, but vestibular function was normal. Although therapy included the administration of steroids, antiviral agents and hyperbaric oxygen, the bilateral hearing loss remained unchanged in these 2 patients. Both required the use of a hearing aid after discharge.