Cavity problem which can develop after an open cavity mastoidectomy have received much attention in the field of otology. Such cavity problem occurs when squamous debris accumulates in the newly formed cavity. Recently, the morphology of this newly formed skin in the open mastoidectomized cavity was investigated to compare with that of the cholesteatoma matrix. The aim of this study was to compare the cytokratin pattern of the cavity skin with that of middle ear cholesteatoma and ear canal skin, and to seach the pathogenesis of cholesteatoma. In this study, we investigated cytokeratin expression of the cavity skin, cholesteatoma matrix, postauricular skin, middle ear epithelium and ear canal skin, using an immunohistochemical technique with five subtypes of monoclonal anti-epithelial keratin. Similaity of cyokeratin patterns was observed among cavity skin, middle ear cholestetoma and ear canal skin. These findings support the skin type epithelial origin of cholestatoma and strongly favor the immigration theory in the genesis of cholesteatoma.