A histologic evaluation of the accuracy of TMJ diagnostic arthroscopy. Sixty-seven temporomandibular joints with internal derangement were examined with arthroscopy, and synovial biopsies were taken for histologic evaluation. Histologically, in 10 cases, the synovium appeared to be normal in appearance, 24 cases had moderate to severe synovitis, 11 cases showed hyperplastic synovitis, 13 cases showed synovial fibrosis, and foreign body granuloma was found in 9 cases. Correlation between arthroscopic observation and histologic findings disclosed an 89.1% specificity and 100% sensitivity. 