Alterations in the dimensions of the basilar membrane and spiral ligament have been implicated in the pathogenesis of sensorineural hearing loss in otosclerosis. The histopathological findings in nineteen temporal bones with otosclerotic involvement of the cochlear endosteum are reviewed. Hyalinization and decrease in the width of the spiral ligament are the only consistent findings related to the otosclerotic focus in these temporal bones. The width of the basilar membrane is normal. The hair cell population and the stria vascularis are normal for the age group.