Abstract: Objectives: To compare the differences in diagnosis of regional nasopharyngeal carcinoma among CT, MRI and PET-CT and to explore the value of using ¹⁸F-PET-CT detection for nasopharyngeal carcinoma (NPC). Methods: Between December 2003 and August 2005, 53 patients with NPC who were treated in our hospital were enrolled in the study. Before treatment, contrast-enhanced CT, MRI and ¹⁸FDG-PET-CT scanning were performed. Film reading of CT, MRI and PET-CT was conducted to determine the extent of regional invasion of NPC. Results: Among 53 patients, positive detection rates of retropharyngeal lymphatic metastases were 58.5% (31/53), 67.9% (36/53) and 37.7 % (20/53) based on CT, MRI and PET-CT, respectively. The detection rates of CT and MRI scans were markedly higher compared to that of PET-CT (P=0.02,P=0.001) but there was no significant difference in the positive rate of detection between CT and MRI (P=0.314). The retropharyngeal lymphatic metastasis (RLM) with a maximum transverse diameter of less than 1 cm could be found by CT and MRI, but not PET-CT. Neither the RLMwith a maximum transverse diameter of less than or equal to 0.5 cm nor that with an overt liquefied necrosis could be found by PET-CT scanning. There was no obvious difference among CT, MRI and PET-CT in the ability to detect invasion into other tissues, such as the nasal cavity, oral pharynx, parapharyngeal space, carotid sheath area, infratemporal fossa, sphenomaxillary fossa and sclerotic invasion of the basion. For detection of cavernous sinus and nasal sinuses, MRI may be superior to CT and PET-CT. Conclusions: PET-CT is inferior for detecting local encroachment of NPC, compared to CT and MRI. For the detection of RLMwith a maximum transverse diameter of less than 1 cm, the detection rate of PET-CT is obviously lower compared to CT and MRI. For the detection of RLMwith a maximum transverse diameter of less than or equal to 0.5 cm or with concurrent liquefied necrosis, PET-CT has even more limitations and shortcomings.