Temporomandibular joint dysfunction is a very common problem, estimated to affect 20-30 per cent of the population. The causes are mostly orthopaedic in nature, as with other joints in the body, but may involve rheumatoid disease, nerve entrapment, infection or tumour. The author guides readers through the wide range of presenting signs and their causes, in adults and children. Illustrations demonstrate the use of conventional radiography, arthroscopy, videofluoroscopy, CT and MRI in investigating these conditions and planning their treatment.