Hearing loss due to malformations of the auditory system may involve morphologic abnormalities of the external canal, the middle ear, or the inner ear. Various combined malformations are possible. Audiologic assessment and computed tomography make it possible to perform a precise diagnostic evaluation of inner ear malformations. In a series of 71 children with congenital sensorineural hearing loss, 31 had computed tomographic evidence of malformations. Since 19 children had bilateral lesions, a total of 50 ears were studied. The cochleovestibular abnormalities were typed and correlated to the severity and progression of hearing impairment. The 3 most frequently encountered malformations were: 1) isolated large cochlear aqueduct (n = 12), 2) large vestibular aqueduct (n = 8) and 3) the Mondini malformation (n = 7). The most severe hearing losses were associated with cochlear hypoplasia and incomplete cochlear segmentation. The severity of hearing impairment decreased with the following abnormalities in the order given: 1) large cochlear aqueduct, 2) Mondini malformation and 3) large vestibular aqueduct. Among the 15 patients with progressive hearing loss, 13 had large cochlear aqueducts either isolated or concomitant with other lesions. While certain evident abnormalities, such as cochlear aplasia or Mondini malformation, are relatively easy to diagnose, other more subtle morphologic changes, such as large cochlear aqueduct, still need to be better defined according to precise criteria for radiographic evaluation.