Objective To compare the temporomandibular joint space and condylar position on transcranial projections between the patients with anterior disc displacement（ADD） and the healthy controls. To investigate the diagnostic value of the condylar position for the ADD patients. Methods 120 joints of 120 ADD patients and 30 joints of healthy adults, who were taken transcranial projections , were included in this study. The transcranial projections were scanned with precise scanning apparatus and saved as joint photographic group image. The joint spaces were measured with the software of Auto CAD. Two different quantitative methods of joint space measurement, ZHANG Zhen -kang′ s method and Kamelchuk′ s method, were used based on the transcranial projections . The ln（P/A） values were calculated（P：width of the posterior joint space; A: width of the anterior joint space）. Concentric position of the condyle was defined if ln（P/A） value was between -0.25 and +0.25. If ln（P/A） was larger than +0.25, the condylar position was defined as anteriorly eccentric. Posteriorly eccentric position was indicated when ln（P/A） value was lower than -0.25. The results were compared and software SPSS 12.0 was used for statistical analysis. Results The results of the two linear measurement methods demonstrated that the superior and posterior joint spaces of the ADD patients were narrower than those of the healthy controls significantly（P0.05）. In addition, there were significant differences in ln（P/A） values of joint spaces between the patients with ADD patients and the controls （P
