A retrospective study of computed tomography scans of the paranasal sinuses of 131 control subjects in Hong Kong revealed minor mucosal abnormalities in more than half of the ethmoid sinuses. Major abnormalities were present in seven per cent of maxillary, five per cent of anterior ethmoid and four per cent of posterior ethmoid sinus. In 85 patients with nasopharyngeal carcinoma the prevalence of minor mucosal abnormalities in the sinuses was similar to that of the control group but major mucosal abnormalities were significantly more common in the anterior and posterior ethmoids at 15 per cent and 21 per cent of the respective sinuses (p < 0.001).