A postmortem study was performed on the bilateral temporal bones of a 90-year-old woman who had a lifelong profound hearing impairment. The histopathologic findings included severe Mondini dysplasia with unusual enlargement of the vestibular aqueducts and endolymphatic sacs. Dehiscent carotid arteries and dehiscent facial nerves were also present. The clinical and surgical aspects of the case are discussed based on the histopathologic findings. The physician should be prepared to diagnose congenital hearing impairment promptly to avoid complications during the clinical and surgical treatment of patients with Mondini dysplasia.