Nasopharyngeal carcinoma (NPC) is endemic in southern China, and its incidence 
in Hong Kong is relatively high. Radiotherapy is the mainstay treatment for NPC 
due to its relatively high radiosensitivity and deep-seated anatomical position, 
which is not readily accessible by surgery. Although the technique of 
radiotherapy in NPC has been advancing and offers promising treatment outcome, 
complications around the irradiation areas are inevitable and the quality of 
life of the post-radiotherapy patients is often compromised. Trismus, which is 
defined as the restricted mouth opening or jaw movement due to the disorder of 
temporo-mandibular joint (TMJ), is one of the possible late complications for 
radiotherapy of NPC and is found in 5-17% of the post-radiotherapy (post-RT) 
patients. Trismus at early stage may only affect the speech, but in severe cases 
nutritional intake and oral hygiene condition may deteriorate seriously. This 
article reviewed the possible causes of radiation-induced TMJ damage, the 
various assessments including imaging modalities and possible treatments. The 
conclusion is that the availability of simple, yet effective examinations for 
trismus is essential for delaying the progression and restoring TMJ functions. 
Although there is no absolutely effective treatment for trismus, many 
supportive, restorative and palliative management are possible under different 
clinical situations.