Purpose: The purpose of this study was to compare the clinical and radiographic features of temporomandibular joint (TMJ) osteoarthritis (OA) between adolescents and middle-old aged patients. Methods: The subjects were chosen among the patients who presented to the Department of Oral Medicine of Pusan National University Hospital and were diagnosed with TMJ OA by clinical exam, X-ray and cone-beam computed tomography (CBCT) from 2010 to 2011. We investigated 93 adolescent patients (12-19 years) and 53 middle-old aged (>45 years) patients who observed the erosive bony changes in TMJ. CBCT scans were retaken at intervals at an average of 8 months. Results: The adolescent patients showed unilateral degenerative changes more often, and the middle-old aged patients showed degenerative changes more frequently on both sides. The transition of bone changes to the improved group occurred most commonly in both the adolescent and middle-old aged patients. The adolescent patients were more likely to improve than middle-old aged patients. In the adolescent patients, loss of erosion and subjective symptoms occurred in shorter periods than in the middle-old aged patients. In the adolescent patients, the transition of erosion was distributed into proliferative, normal, and shortening in order. In the middle-old aged patients, the transition of erosion was distributed into shortening, proliferative, and normal in order. Conclusions: The clinical and radiographic features of TMJ OA are a significantly different between the adolescent and middle-old aged patients. Moreover, the difference by age of the adaptive and regenerative capacity of TMJ affects the prognosis of TMJ OA and adolescent patients have a better prognosis after treatment.