By reviewing retrospectively the HRCT findings in 130 surgically proven cases of chronic otitis media with cholesteatoma, we estimated the sensitivity, specificity, and positive predictability of the HRCT compared to surgical findings. For exposure of the facial canal, the sensitivity, specificity, and positive predictability was 59.7%, 84.9/% and 85.2% respectively. For exposure of the lateral semicircular canal, the sensitivity was 80.6%, the specificity 99.0% and the positive predictability 96.2%. Conclusively, the diagnostic accuracy of preoperative temporal bone CT regarding the state of the lateral semicircular canal seems to be highly reliable. Gross invasion of the facial canal can be usually detected. However, relatively low sensitivity suggests that evaluation of the ultra-thin structures of the tympanic segment is often problematic.