We performed standardized anterior-posterior radiographs of the normal ankle on 50 males and 50 females to determine the validity of current radiographic landmarks of the ankle syndesmosis separation. The average tibiofibular overlap was 6.9±2.1mm. The tibiofibular clear space was measured 4.1±0.9mm overall. The ratio of the tibiofibular overlap to the fibular width averaged 48±14%. Our data show that for 95% confidence intervals, the values for the syndesmosis separation are : (1) tibiofibular overlap less than 2.7mm, (2) tibiofibular clear space greater than 5.9mm, (3) tibiofibular overlap: fibular width ratio less than 24%. According to current diagnositc criterion of tibiofibular overlap under 10mm, 87% of this cohort was defined as syndesmosis separation. Other current criteria of tibiofibular clear space over 5 mm and tibiofibular overlap: fibular width ratio less than 24%, the false positivity was only 7% and 2%, respectively. Therefore the tibiofibular clear space and the tibiofibular overlap: fibular width ratio are more reliable diagnositc criteria for syndesmosis separation than the tibiofibular overlap.