High resolution temporal bone computed tomography(TBCT) reveals inner ear structures well. It helps in detecting inner ear deformity that might occur from teratogenic influences during the first trimester which cause arrest in development of the inner ear. It also has an essential role in selective preoperative assessment of cochlear implantation. A prospective study on TBCTs of children with bilateral sensorineural hearing loss(SNHL) was performed to determine the prevalence and to reveal findings of inner ear malformations. TBCTs of 118 children with SNHL who visited our children's hospital between August 1989 and December 1992 were taken and their medical records were reviewed. TBCTs of 25 children with unilateral cholesteatoma without any known SNHL were reviewed as a normal control group, and measurements from this group were used as normal standards. Abnormal TBCT findings were as follows : cochlear hypoplasia such as Mondini's aplasia ; increased vestibular width ; hypoplasia of lateral semicircular canal ; widening of internal auditory canal ; widening of vestibular aqueduct ; widening of cochlear aqueduct ; and miscellaneous. Of great concern is that 22 out of 118 children with SNHL(19%) had abnormal TBCTs, among which 11 children(9%) had Mondini's anomalies.