OCALIZED osseous dystrophy of the L Iabyrinthine capsuIe or histoIogic otosclerosis, when uncompIicated by tympana1 pathoIogy, is not diffIcuIt of diagnosis after invoIvement of the hearing mechanism has occurred. Yet it may exist throughout Iife and be impossibIe of recognition if hearing is normaI. Of great importance is the age of onset and the progressiveness of the impairment. RecentIy a 68 year old man, with hearing markedly impaired, showed a typica nerve deafness audiometric curve with moderate impairment for Iow frequencies. A so-caIIed seniIe atrophy of the spira1 gangIion wouId have been the diagnosis had not the famiIy history and the age of onset (22 years) been in favor of otosclerosis. His focus at the site of prediIection (anterior to the ova1 window) was undeveIoped, whiIe probably a round window patch had grown into the cochIea in the high tone area. Such cases are not uncommon. AIthough otoscIerosis is a regressive hereditary maIady, we must not Iose sight of the fact that otoscIerotic bone is under the same influences that contro1 norma bone growth. This expIains the cIinica1 manifestation at the end of adoIescence. It has been shown by Guggenheim, Bast, GuiId, Siebenmann and Manasse that the osseous dystrophy begins many years before an impairment of hearing is noticed. One reason for this is that peopIe are usuaIIy not examined unti1 the hearing impairment is greater than the intensity of conversation voice and interferes with the routine of Iife. In the Deafness Prevention Centre in Los AngeIes, where supposedIy norma chiIdren from 4 to 16 years oId are being studied, the very first patient was the “normaI” 7 year oId daughter of an otoscIerotic woman. This patient showed impaired hearing with the audiometer and other signs of an earIy otoscIerosis. The dystrophic bone constituting the otoscIerotic focus is Iaid down during the feta1 period and Iater is subjected to the same stimuIi from thyroid and pituitary hormones that a11 bone receives. The steady increase in the size of the focus finaIIy resuIts in invoIvement of the annuIar Iigament, etc. The pink shimmer sign is seIdom seen, but when present is pathognomonic. It is not usuaIIy due, as is commonIy thought, to the high vascuIarity of the porous bone of the focus, but rather to the engorged capiIIaries of the mucoperiosteum of the tympanic cavity overIying the focus. When uncompIicated, typica otoscIerosis manifests the foIIowing signs: (I) decrease or absence of cerumen; (2) biIateraIity; (3) defective or absent vasomotor response of the drum membrane; (4) norma drum membrane with norma mobiIity of membrane and maIIeus; (3) patent Eustachian tubes; (6) negative Rinne test; (7) proIonged Schwabach test; (8) paracusis wiIIisii; (9) varying degrees of tinnitus and throbbing; (IO) sIight pain in a smaI1 percentage of cases; (I I) pink shimmer in a few cases; and (12) norma bone conduction with varying degrees of conduction impairment. The air curve may show invoIvement for Iower frequencies and a gradua1 sIant to norma for high tones, but more frequentIy it is a Iine st’raight across. Where the round window and interna meata foci are present, there may