The clinical significance of the middle ear cholesteatoma lies in its association with progressive bone destruction which requires major middle ear surgery for eradication of the pathological lesion. Otologists have been engaged in a search for answers concerning the pathogenesis and pathophysiology of cholesteatoma since its early descriptions by Cruveilheir and Mueller, and much information has been gathered over the past 140 years. Although several theories have been formulated, the exact pathogenesis of this disease is still to some extent unknown. Recent advances in immunology have opened a new approach to investigating the etiology and pathogenesis of aural cholesteatoma by the immunohistochemical technique. Immunohistochemical and submicroscopic analyses of human cholesteatoma matrices revealed the presence of Langerhans' cells which probably play a key role in the pathogenesis of this disease. Several reports have suggested that Langerhans' cells in cholesteatoma are significant and that the pathogenesis of this disease with bone resorption could be explained by cell-mediated immune response, but there is still some controversy. The aim of this study was to measure the number of Langerhans' cells in the middle ear cholesteatoma through the immunohistochemical technique and to compare them with those in postauricular skin. The results obtained were as follows : 1) The Langerhans' cells in cholesteatoma increased significantly compared to those in the postauricular skin (p<0.05). 2) The Langerhans' cells in the cholesteatoma matrix had more numerous and longer dendritic processes than those in the postauricular skin.