Purpose The computed tomography (CT) is an excellent technique for the evaluation of the middle ear (with detailed demonstration of the ossicular anatomy). CT also was shown to depict otoscleotic foci early in the course of the disease. This technique has thus an increasing role in the evaluation of the conductive hearing loss (CHL) as a noninvasive alternative to exploratory tympanotomy. The aim of this study was to evaluate the reliability of CT findings in predicting the etiology of CHL, to correlate the degree of radiologic abnormalities with the audiological findings and to investigate the value of tomographic measurements as a preoperative guide before tympanotomy. Materials & Methods Forty-three patients (45 ears) were evaluated prospectively with preoperative audiometric evaluation and temporal bone CT, followed by exploratory tympanotomy. External auditory canal diameter (EACD) was measured by CT on the sagittal and coronal reformats and compared with speculum diameter used in surgery (Figure A). Similarly, incus long process -stapes footplate distance were measured with CT on the Poschl reformatted images (Figure B) and compared with the Teflon piston size used during surgery. In cases with otosclerosis, the otosclerotic focus was measured on CT, classified according to Symons and Fanning and was compared with the audiological data. Results At surgery, otosclerosis was found in 39 ears. In the remaining 6 ears the underyling pathologies were ossicular anomalies with absence of stapes suprastructure, deficiency of the long process of incus, fracture of stapedial crura and fusion of the malleolus. Superior semicircular dehiscence was not detected. 42 of 45 ears were correctly diagnosed with the CT scan (with a sensitivity of %93.3). The detection of otosclerosis