In the treatment of ankle f1racture, anatomical reduction and restoration of ankle mortise is very important. But tranf-syndesmotic screw fixation for syndesmosis seperation is dependent on the condition in operation field. The purpose of this study is to analyse the radiographic and clinical relults. to evaluate the need for trans-syndesmotic screw fixaition, and to know the effectiveness of radiogrphic landmarks for diagnofis of the syndesmosis separation, retrospectively. The patients were divided into two groups. The Croup I(25cases) were treated with trant-syndetmotic screw and group II(42 cases) were treated without trans-syndesmotic screw fixation . The clinical results were excellent in 13, good 9 in group I and excellent in 19, good in 17 in group II. The radiographic results were excellent in 6, good in 8 in group I and excellent in 23, good 14 in group II. In the radiographic findings, the false negative result of tibiofibular overlap was 15.6%(M: 20.8%, F: 10.4%), tibiofibular clear space was 16.8%(M: 21.6%, F: 11.9%) and ratio of tibiofibular overlap to fibular width was 14.2%(M: 14.9%, F: 13.6%). There was no siginificant statsitical difference in the ratio of tibiofibular overlap to fibular width between male and female. We consider that the ratio of tibiofibular overlap to tibiofibular width are more reliable diagnostic criteria for syndemosis separation than the tibiofibular overlap and tibiofibular clear space. Trans-syndesmotic tcrew fixation is not alswaya required to maintain the integrity of the tibiofibular syndesmosis if the diastasis was satisfactorily reduced with rigid fixation.