High resolution computed tomography (HRCT) of the temporal bone is performed routinely in the preoperative evaluation for cochlear implantation. The largest multicentre retrospective analysis of data was undertaken to compare the findings on HRCT with the surgical findings in an attempt to determine the accuracy of HRCT. Of the 1009 patients referred, 525 were scanned of whom 335 were implanted. As part of this study we were also able to identify both radiological and non-radiological reasons for rejection of patients for cochlear implantation. the commonest cause being adequate residual hearing. The accuracy of HRCT in predicting cochlear ossification was 94.6%, with a 100% specificity and a 71%, sensitivity. Meningitis was the leading cause of cochlear ossification (44%). We conclude from this extensive multicentre study of both adult and paediatric patients that HRCT is accurate in predicting cochlear abnormality. In post-meningitic patients magnetic resonance imaging (MRI) may be a useful additional investigation.