The lateral syndesmosis malleolar complex is a factor of importance for congruence and stability of the ankle joint. The failures of function due to excessive talar motion or instability and incongruity, predisposes the osteoarthritis of ankle joint. The authors analysed 46 cases of lateral malleolar fracture with diastasis in our department during the years 1976 through 1986. The results obtained are as follows. 1. The most common cause of injury was slipping down and the other causes were falling down and traffic accident in order. 2. The types by Weber classification showed 21 cases of type BS(+) and 25 cases of type C. The most common type by Lauge-Hansen classification was supination-external rotation type(21 cases, 45.7%). 3. Partial diastasis was noted in 25 cases(54.3%) and total diastssis in 21 cases(45.7%). 4. Open reduction was performed in 43 cases. For the treatment of diastasis, 20 cases were treated with transfixation screws, 9 cases with repair of anterior inferior tibiofibulsr ligament and 11 cases with both method. 5. According to colton's criteria, the result was good in 24 cases(65%), fair in 10 cases (27%) and poor in 3 cases(8%). 6. The incidence of traumatic arthritis was 29.7%(11 cases).