The clinical and histologic features of the second reported case of retrotympanic odontoma, which clinically presented as a cholesteatoma, are described. Origin from the posterior extension of the dental lamina is postulated. The dental lamina, the thickened oral ectoderm which outlines dental structures, is incorporated subendodermally in the lateral outpouching of the first pharyngeal pouch which produces the middle ear cavity. Histologically the odontoma was "complex," containing a haphazard arrangement of cementum, dentin, dental follicle and proliferating dental lamina, without the formation of recognizable teeth.