17 new cases of malformation of the bony labyrinth detected radiologically (tomography, CT) and associated with perceptive or composite deafness are reported. 2 cases discovered in spontaneous or traumatic recurrent meningitis are described, as well as 1 case discovered after the occurrence of total deafness following stapedial surgery. The malformations were unilateral in 7 cases, bilateral in 10. Deafness was of the composite type in 6 cases. An associated malformation of the middle or external ear was noted in 4 cases. 5 cases were included in a context of multiple malformations, including 1 case of otobranchiorenal syndrome, 1 case of Apert's syndrome and 3 cases of craniostenosis. Referring to the classification given by Mrs Vignaud and Jardin, we have encountered 1 case of stage I malformation, 9 cases of stage II, pseudo-Mondini malformation, 1 case of stage III or true Mondini malformation, 1 case of stage IV malformation, 3 cases of malformation of the aqueduct of the vestibule, ie. stage V. We have also encountered 2 isolate cases of stenosis of the internal auditory canal. On the basis of these cases, we report a few physiopathogenetic hypotheses and various classifications currently described in the literature. We also list the various associated external and middle ear malformations and the multiple-malformation syndromes that are commonly described. Stress is laid on the fact that these malformations often go undetected in congenital deafness, as well as on the usual course of these types of deafness for which there is no medical or surgical treatment.