To evaluate the usefulness of quantitative analysis of computed tomographic images in diagnosing stapedial otosclerosis, high-resolution temporal bone computed tomography (CT) of 32 ears with otosclerosis and 19 control ears was used. The images on the section containing the oval window were digitized using a scanner, and the ratio of the mean gray scale value of 5 areas in the otic capsule including the area anterior to the oval window to that of the cortical bone was calculated. The mean value of the ratio of the area anterior to the oval window was significantly lower in the otosclerosis group (0.85 ± 0.10) than in the control group (1.03 ± 0.03; Student t test: t = 7.94, p < 0.0001). In 30 of 32 (93.7 %) otosclerotic ears, the values were lower than the normal range calculated in the control group. This method of quantitative CT image analysis comparing the area anterior to the oval window was considered useful in diagnosing stapedial otosclerosi