Osteochondrosis dissecans (OD) and synovial chondromatosis (SC) are two rare causes for loose bodies in the temporomandibular joint. It is assumed that OD is a reaction of some type of joint trauma. Gene mutations similar to what is known in chondrosarcomas can be found in metaplastic SC. The reasons for mutations are still unknown. Both diseases have very similar symptoms. Patients suffer from preauricular swelling, facial or temporomandibular joint pain, and occasional joint locking. In addition, radiological imaging (MRI) is difficult in evaluating the differential diagnosis of presented intra- or periarticular pathology. To overcome diagnostic problems, we strongly support temporomandibular joint arthroscopy as a diagnostic and therapeutic tool. The decision whether or not total synovectomy is needed or if simple removal of fragments is adequate can be evaluated in vivo including the option of histopathological examination.