The pathologic conditions that involve the TMJ are similar to those conditions that involve other joints in the body. Therefore, many of the radiologic characteristics of these diseases are also similar. Nevertheless, because the articular surface of the condyle is an important site of mandibular growth, leading to secondary facial asymmetries when damaged in young patients, this possibility must be considered when evaluating the radiographic changes. It also is important to understand that functionally the TMJs act as a single unit and that any alteration in function caused by a pathologic process on one side can lead to disturbed function on the opposite side. Such dysfunction can cause degenerative changes that must be distinguished from the primary disease. Finally, some of the conditions that involve the TMJ can produce rather similar radiographic changes. In these instances, an understanding of the associated clinical findings can be helpful in making a more accurate radiographic diagnosis.