We have compared two techniques of arthroscopic surgery for advanced internal derangement of the temporomandibular joint (TMJ). Patients with stage III or above TMJ internal derangement, who had not responded to three months of non-surgical treatment, were prospectively and randomly assigned to one of two types of treatment. One group had arthroscopic lysis and lavage (ALL) and the other had ALL plus arthroscopic anterolateral capsular release (AALCR). All patients were assessed preoperatively, and at 1, 3, 6, and 12 months postoperatively. Thirty-five patients (41 joints) had ALL and 66 patients (73 joints) had AALCR. The only significant difference was at 1 month, when the ALL group could not open their mouths as far as the AALCR group (P < 0.01). Both groups had significantly less pain in the joint and better jaw opening one year postoperatively. The stage of disease did not affect the outcome. Both ALL and AALCR gave good results in the management of advanced internal derangement of the TMJ. Unless early wide mouth-opening is required, the less invasive procedure of lysis and lavage should be chosen.