Diagnostic arthroscopy and arthroscopic surgery of the TMJ has during the recent years been introduced in the treatment of internal derangements, preauricular pain and osteoarthrosis of the TMJ. In closed lock cases and in cases with preauricular pain a satisfactory result of treatment has been described in 80-90% of cases, where there was lacking effect of conservative treatment with splints and physiotherapy. The refinement in the technique has made it possible to use rotating instruments, cauterisation and to perform suturing through the arthroscopic cannula and in this way reduce the need for open joint surgery. Due to the technique only few complications have been reported. In the Department of Oral and Maxillofacial Surgery in the University Hospital of Aarhus arthroscopy of the TMJ was introduced 1 1/2 year ago and 22 patients with the clinical diagnosis closed lock or preauricular pain or a combination of these has been treated during this period. The results are satisfactory in most cases and are comparable with previously published results.