Internal derangement of the temporomandibular joint has mainly been studied arthrographically from the standpoint of anterior disk displacement with or without reduction. Frequent clinical observations of disk deformation in joints with internal derangement implied the need for a systematic study of morphologic alterations associated with internal derangement. Therefore, morphology, internal derangement, and joint function were studied in 58 randomly selected autopsy specimens of the temporomandibular joint. The results showed that joints with superior disk position rarely demonstrated morphologic alterations. In joints with partially anterior disk position, disk deformation occurred somewhat more frequently (31%) and was consistently located in the part of the disk that was positioned anteriorly. Joints with completely anteriorly positioned disks showed disk deformation in 77% and irregularities of the articular surfaces in 65%. It appears that anterior disk position precedes disk deformation. Therefore, early causal treatment to correct symptomatic internal derangement appears indicated to decrease the possibility of development of disk deformation. Disk deformation was also closely associated with disturbed joint function and should therefore be an important consideration when one is planning treatment of internal derangement of the temporomandibular joint.