A retrospective study was carried out to determine the prevalence of abnormality in the paranasal sinuses in a British population having magnetic resonance imaging (MRI) scans for neurological signs and symptoms. The T2-weighted scans of 130 patients were studied. Abnormalities in the paranasal sinuses show as high signal on the T2-weighted scans and thus are clearly seen. Abnormalities included mucosal thickening, fluid levels, sinus opacification and retention cysts/polyps. Of the patients studied, 49.2 per cent showed one or more abnormality. Mucosal thickening was the most common abnormality noted and the ethmoid sinuses the most commonly affected.