<b><i>Objectives:</i></b> On computed tomography (CT), sinonasal schwannoma displays as a soft-tissue mass without any distinctive features. Our aim was to define the radiological criteria for distinguishing schwannoma from other sinonasal benign tumours. <b><i>Methods:</i></b> We<i></i> retrospectively identified consecutive patients who were pathologically diagnosed with benign sinonasal tumours between 2007 and 2016. CT attenuation values were compared between benign tumours and the brainstem. The utilities of demographic factors, clinical factors, and CT parameters for predicting the CT attenuation values of the brainstem were analysed by univariate and multivariate regression. <b><i>Results:</i></b> Of the 111 identified cases of benign tumours, the CT attenuation values of tumours and the brainstem were analysed in 36 cases (schwannoma, 4 cases; inverted papilloma, 26; juvenile nasopharyngeal angiofibroma, 3; cavernous haemangioma, 3). The CT attenuation values of the schwannomas were significantly lower than in the brainstem, while those of the other tumours were significantly higher than in the brainstem. No factors affected the CT attenuation values of the brainstem. <b><i>Conclusion:</i></b> Low CT attenuation values of sinonasal benign tumours relative to the brainstem could distinguish schwannomas from other benign tumours.