Purpose: To evaluate the relationship between internal derangement and osteoarthrosis in the temporomandibular joint (TMJ) using magnetic resonance imaging (MRI). Materials and Methods: One hundred and six MR images of TMJs in 53 patients were evaluated. Disc displacements and osseous changes of the TMJs were assessed. Lateral and rotational disc displacements were also evaluated on coronal images. Results: No significant differences in the frequency of osseous changes of the TMJs between disc displacement with reduction and disc displacement without reduction groups were found. The erosion of the condylar head and the sclerosis of the articular eminence were more frequent in the internal derangement group than in the no disc displacement group. The flattening was the most frequently observed osseous change of both the condylar head and articular eminence. Conclusion : The relationship between internal derangement and osteoarthrosis is obscure, but it is thought that both disorders adversely affect each other.