Hugh resolution computed tomography(HECT) of the temporal bone can provide to clinicians precise informations regarding to middle ear pathology. We compared the HRCT findings with operative findings of the middle ear pathology retrospectively in 267 patientss with chronic otitis media who underwent mastoid surgery during the period between Jan. 1987 and Dec. 1992. The results are as follows : 1) Among 250 ears with soft tissue density with bone erosion on HRCT, two hundred four ears revealed cholesteatoma. The predictability was 80.1%. 2) Erosions of ossicles were noted in 241 ears on HRCT, but two hundred fifty ears revealed erosion of ossicles actually. The predictability was 90.6%. 3) In 75 ears there were facial nerve canal erosion on HRCT. Among them, forty seven ears demonstrated canal erosion in operation. The predictability was 84.3%. 4) Thirty-four ears of 42 those were suspected having semicircular canal fistula based on HRCT were proved to have fistula in operation. The predictability was 95.9%. 5) Middle fossa or posterior fosa dural plate erosion was suspected 34 ears on HRCT, but twenty three ears actually have dural plate erosion and the predictability was 88.4%. 6) Among 22 ears those suspected erosion of sinus plate on HRCT findings, thirteen ears found to have erosion of sinus plate.