The principal role of computed tomography (CT) scanning in rhinosinusitis is as a planning investigation for patients requiring functional endoscopic sinus surgery (FESS). The pre-operative scan is used to highlight any potential surgical hazards, and to delineate the extent of disease reducing unnecessary intervention in disease-free areas. It is inappropriate for CT to be used purely as a diagnostic investigation for chronic rhinosinusitis. As concern has been expressed over the steady rise in the referrals for CT of the sinuses, we conducted a retrospective review of all patients having these scans at two CT scanner sites in Scotland during 1993. Of the 162 scans performed for rhinosinusitis, 58 patients (36 per cent) had not had nasendoscopy performed or had a trial of medical treatment. Subsequently, only 61 patients (38 per cent) went on to FESS. The inappropriate use of CT for these patients can be reduced by insisting that nasendoscopy is performed prior to scanning. Furthermore, radiologists and surgeons should audit the number of patients not having FESS after scanning.