Bilateral conductive deafness is common in mandibulofacial dysostosis with or without atresia of the external auditory meatus. This deafness is due to a wide range of deformities of the ossicular chain associated with a characteristic reduction in the size of the middle ear cavity. The inner ear is only occasionally affected. This study describes findings of experimentally induced malformations of the ears in laboratory animals which are compared to the clinical, radiological and surgical findings from 14 patients with mandibulofacial dysostosis (Treacher-Collins syndrome).