Arthrography is one of highly accurate diagnostic tools for internal derangements of the temporomandibular joint (TMJ). Both TM joints are connected by the mandible and one may have influence upon the other. We performed bilateral TMJ arthrograms in 42 patients with TMJ disorders to evaluate the bilaterality of internal derangements of the TMJ. The results were as follows : 1. We could not find any specificity in clinical symptoms according to each state of internal derangements of the TMJ. 2. The bilaterality of internal derangements of the TMJ was 61%. 3. Statistically, significant correlation was found in the aspects of the presence of arthrographic abnormality in both TMJ and each state of internal derangements in them. Therefore, the patients, who are diagnosed as any internal derangement of the TMJ, need to have assured examination in the contralateral joint.