Electron microscopic study of the cochleas of an individual with bilateral Ménière's disease revealed the presence of many abnormal sensory cells in the apical regions of the cochleas. The pathological alterations were greater in the left ear with the greater hearing loss. There were some giant cilia, fusion of cilia, and loss of cilia. The outer hair cells contained diffuse cuticular bodies near or basal to the nuclei. Many outer hair cells were retracted away from the reticular membrane. The population of the nerve endings appeared normal. The inner hair cells of the apical turns appeared essentially normal. The spiral ganglia were normal in number and morphology at the apical turns, and a majority of their cell bodies were of the unmyelinated or partly myelinated types. The stria vascularis showed atrophy; however, the magnitude of this change was consistent with that known to occur in the aging ear. In the distended areas Reissner's membrane showed areas devoid of mesothelial cells, as well as atrophic epithelial cells. The blood vessels were no different from other human cochlear vessels. These abnormalities seen in the stereocilia, the outer hair cells, and Reissner's membrane are a matter of fact. We must admit, however, that not enough electron microscopic studies have been performed on ears from aging individuals or ears with other pathologies to state that these changes are unique to Ménière's disease. Furthermore, there is currently insufficient knowledge to predict whether these changes affect auditory function.