The authorspresent an account on views regarding the development of cholesteatoma behind an intact ear drum which is usually considered primary and congenital, genuine. This view is supportedbythefollowingetiologies ofdevelopment: impaireddevelopmentof thetympanicmembrane (Aimi), metaplasic transformation (Sadé), presence of cellular masses of amniotic fluid (Northrop) and epidermoid formations (Michaels). In 2000 a new theory of development of acquired cholesteatoma behind an intact tympanic membrane in the area of the mesotympanum was published (Tos). The authors, based on their won histological observation of temporal bones of aborted foetuses, support some theories of the development of cholesteatoma behind an intact tympanic membrane - penetration of proliferating epithelium into the middle layer of the tympanic membrane, the presence of cellular masses of amniotic fluid and epidermoid formation located in different parts of the middle ear cavity. In one epidermoid formation keratinization of the surface layer was found. On the clinical material of five patients operated on account of a cholesteatoma without perforation of the tympanic membrane the authors demonstrate possible localizations of a cholesteatoma. The presence of otitis media in the case-history in four of five patients supports the possible postnatal development of a cholesteatoma behind an intact tympanic membrane. Based on investigations of temporal bones, clinical experience and publications in the literature the authors recommend a classification of cholesteatomas. The latter are classified according to the state of the tympanic membrane: 1. behind an intact tympanic membrane (primary cholesteatoma) or 2. with a defect of the ear drum (acquired cholesteatom). Behind an intact tympanic membrane is a (1a) congenital cholesteatome which develops probably on the basis of one of the following possibilities - epidermoid formation, cellular masses of amniotic fluid and proliferation of the epithelium across the tympanic membrane or (1b) acquired cholesteatoma the etiology of which can be explained by the inclusion theory or metaplasia of the middle ear mucosa. Acquired cholesteatomas with a defect on the tympanic membrane can be divided into (2a) primarily acquired which develop on the basis of a meso- or epitympanic retraction pocket (pseudoperforation) and (2b) secondarily acquired with a true perforation of the tympanic membrane.

        Key words: cholesteatoma, congenital cholesteatoma, etiology, histology, temporal bone.