In a prospective study comparing computed tomography (CT) and magnetic resonance imaging (MRI) in the staging of nasopharyngeal carcinoma (NPC), 17 (15%) patients were noted to have infiltration of the pterygopalatine fossa (PPF). The recognition of PPF abnormalities depends on the familiarity of the normal anatomy. CT and MRI appearances of the normal PPF in the remaining 97 (85%) patients were reviewed. The fossae were symmetrical and fat was seen in all MRI and in 95% of the CT scans. There was destruction of the pterygoid process in 10 (9%) patients and a further 10 patients showed erosion of the maxillary sinus. Superior infiltration from the PPF into the inferior orbital fissure was demonstrated in 7 (6%) patients. Lateral spread via the pterygopalatine fissure into the infratemporal fossa could be seen in 10 (9%) patients. The earliest indication of tumour infiltration of the PPF is the replacement of the normal fat content. Widening of the fossa and erosion of the bony margins are late signs. As expected, bony abnormality is best seen on CT. However, direct visualisation of tumour or replacement of fat is more elegantly demonstrated on T1-weighted MRI.