We report the clinical and otopathologic findings in three persons from two kindreds affected with adult-onset autosomal dominant progressive sensorineural hearing loss. The primary pathologic change is a deposit of acid polymucosaccharide ground substance in the cribrose areas; in the spiral ligament, limbus, and spinal lamina of the cochlea; and in the stroma of the maculae and cristae. These deposits obstruct the channels that accommodate the dendritic nerve fibers to the auditory and vestibular sense organs. The end result is strangulation and degeneration of dendrites followed by retrograde neuronal degeneration in association with varying degrees of atrophic change in the sense organs.