The term 'endolymphatic hydrops' is not a definitive diagnosis since the condition occurs in a variety of otological disorders. Endolymphatic hydrops was found in 57 ears (9 per cent) of the 703 temporal bones in the collection of the Ear Research Institute, Los Angeles. These 57 ears included normal ears of two newborns, post-stapedectomy ears, and ears with the primary diagnosis of Menière's disease. Paget's disease, congenital syphilis, and chronic otitis media. The typical clinical picture of fluctuant hearing loss, pressure, tinnitus, and episodic vertigo occurred in about one-third of the cases with histologically documented hydrops. This symptom complex was common in cases with diffuse, bilateral, cochleo-saccular, or progressive hydrops. A reliable clinical test to determine the presence of endolymphatic hydrops is needed. Complete neurotologic evaluation is indicated in every case suspected of having hydrops to determine specific causes.