Purpose: This study was aimed to investigate the relationship between the mandibular asymmetry and the internal derangement of temporomandibular joint. Materials and methods: One hundred and sixty eight patients had been assessed through clinical examinations, panoramic radiographs and magnetic resonance imagings (MRIs), were selected. The samples were classified into three subgroups according to the severity of the mandibular asymmetries in the panoramic radiographs and the status of TMJ discs on the MRI were compared among each groups. Results: In an apparent asymmetry group, there was a significant difference in the number of temporomandibular disk displacement without reduction between the long and short side (66.7%, 18/27 joints on the short side) when the ratio of condylar process and coronoid process was used (p<0.05), but there was no statistically significant difference when the ratio of condyle and ramus was used. Conclusion: The probability of the disc displacement without reduction was higher at the side with relatively shorter condylar process on the panoramic radiograph, and also it might be more effective to use ratio of condylar process and coronoid process in the assessment of mandibular asymmetry. Therefore, a careful assessment on the temporomandibular disorders is necessary to diagnose and establish the treatment plans for the patients with a mandibular asymmetry and the panoramic radiograph can be used effectively on that way.