Chronic otitis media had been one of the most prevalent forms of infectious diseases in the ENT field. But, recently, the incidences of chronic otitis media have decreased owing to better economic status and health care. Thus, cases of middle ear surgery have also decreased relatively in number. So it seems that otologists nowadays should be engaged in a search for the answer concerning the cavity problems which can occur under conditions of previously performed open cavity mastoidectomy. The aim of this study was to investigate the histology of the newly formed skin in the open-mastoidectomized cavity(cavity skin) through light and electron microscopic studies and eventually to evaluate its usefulness during revision surgery. The authors analysed 15 revision cases of previous open cavity mastoidectomy with the histopathological and ultrastructural features. The results obtained were as follows : 1) In the newly formed skin in the open-mastoidectomized cavity as well as in the cholesteatoma matrix, the presence of hyperkeratosis and exocytosis were noted, which were directly related to the degree of subepithelial inflammation. 2) In contrast to the cholesteatoma matrix, melanin granules were observed in about half the cases of the newly formed skin in the open-mastoidectomized cavity, which was suspected to be related to the degree of subepithelial inflammation and the duration of time which had lapsed since the first operation.