The so-called labyrinthine otosclerosis is defined as a focal otosclerotic involvement of the labyrinthine capsule without stapes fixation. It produces a pure sensorineural hearing loss. The histology of this phenomenon is well known. The relative frequency of labyrinthine otosclerosis is between 4 and 40%, as referred in literature. On x-rays, an advanced demineralisation or complete obliteration of labyrinthic bone is suspicious of otosclerosis. There is no typical pattern of sensorineural hearing loss. But not seldom a fair discrimination index contrasts with a severe threshold evaluation in pure tone audiometry. 208 audiogramms of otosclerosic ears verified by stapedectomy were examined. After correction for normal presbyacusis the sensorineural hearing loss due to otosclerosis is twice that of presbyacusis. In otosclerosis tinnitus is often reported as of metallic type, but a characteristic tinnitus does not exist. There is no universal agreement about the relative frequency of vestibular disturbances in otosclerosis. One should diagnose labyrinthine otosclerosis only if several criteria found are not explanable otherwise, and these criteria are explained.