Magnetic resonance imaging is able to demonstrate a wide range of sinus abnormalities. Incidental findings in patients referred for neuroradiology because of suspected intracranial pathology are surprisingly common and were present in 37.5 per cent of 483 images examined. The maxillary and ethmoid sinuses were most commonly affected with 27 and 26 per cent of images abnormal whereas the frontal and sphenoid sinuses were less commonly affected with 5 per cent of each abnormal. If minor changes were excluded then 17 per cent of patients had either fluid, a polyp or marked mucosal thickening in at least one sinus. Nasal symptoms, other than the presence of a cold, showed no statistically significant relationship to abnormal findings. Many people with inflammatory changes in their sinuses demonstrated on MRI do not have symptoms classically attributed to sinusitis.