Plain radiographs such as Water’s view and the Caldwell view, were once the mainstay of diagnosis of sinus disease, but have now been replaced by high-resolution CT (HRCT) for the evaluation of sinus inflammatory disease. Plain radiographs do not allow adequate evaluation of the ostiomeatal complex or of the sphenoid and ethmoid sinuses, because of overlapping structures. High resolution CT scanning provides excellent bone detail and accurate soft tissue mapping. CT is the modality of choice for imaging inflammatory disease of the sinuses and the ostiomeatal complex. MRI best assesses intracranial complications of inflammatory diseases. For sinonasal tumours, both CT and MRI provide information that is complementary. CT provides bone detail and anatomic landmarks at the skull base, while MRI has the potential to differentiate tumour from adjacent inflammation. Soft tissues are more clearly imaged by MRI and most tissues can be more accurately differentiated as being infected, neoplastic or haemorrhagic, than by CT scans. High resolution CT is used routinely before endoscopic surgery to evaluate the extent of the inflammatory disease and to assess important anatomic landmarks and their variations. Normal appearance and pathology in the PNS is discussed as seen on plain radiography, CT scan and MRI.