Abstract The insertion of the anterior temporomandibular joint capsule at the temporal bone constitutes an anatomic boundary of the joint. When condylar translation exceeds this site, the joint is classified as hypermobile. In this study, the distance from the apex of the articular eminence to the antero-superior capsule insertion was assessed in double-contrast arthrotomograms from 192 joints with and without disc displacement. Maximum condylar translation was also measured. The insertion point of the antero-superior capsule was, on the average, located 4.4 mm (SD, 1.7 mm) anterior to the apex of the eminence, regardless of disc position. Hypermobility was present in 56 joints. Sixty-eight percent of the hypermobile joints had a reducing disc and 62% of all the joints with a reducing disc were hypermobile. In joints with permanent disc displacement, the condyle generally was halted posterior to the apex of the eminence, but could pass extensively anterior to it. Condylar hypermobility thus does not exclude the presence of a permanently displaced disc. In 71% of patients with hypermobility, the condition was bilateral. Because of the close topographic relationship between the joint and nerve branches in the anterior vicinity of the joint, a hypermobile condyle may mechanically irritate the masseteric and deep posterior temporal nerve branches.