The goal in treatment of ankle fracture is the restoration of normal ankle function. Although controversy still exists over the best method of treatment, recent ariticles emphasize importance of the anatomic reduction of fibula and the benefits of early mobilization when adequate fixation is accomplished. When we fix fracture of lateral alleolus with plte and screws, the distal screws should engage the medial cortex of the fibula but not protrude into the talofibular joint. Because the penetration of screws into ankle joint may be the cause of postoperative pain and opst-traumatic arthritis. This article has reviewed a series of 36 ankle fractures, treated from March 1993 to January 1997, using plate and screws. In order to analyse the influence of the penetration of screws into the ankle joint, all fractures were classified according to the penetrating length of screw from medial cortex of lateral malleolus. Thse with the end of the screw protnided more than 2mm into joint were clssified group I, those with less than 2mm groupp II, those with no engagement group III. The results obtained from this study were as follows: 1. According to clinical and radiolgraphic assessment of the results of the treatment, open reduction and internal fixation using plate and screws in treatment of lateral malleous was a satisfactory method. The excellent or good results were achieved in 28 patients among the 36 patients (77.8%). 2. Average time of bony union was not different significally among the three groups. 3. The gain of full range of motion was delayed in group I. 4. Patients of group I complained persistent pain and discomfort more frequently than the other groups. 5. In the treatment of lateral malleolar fracture, the distal screws should engage the medial cortex of fibula to gain firm fixation,but should not protrude more than 2mm into the ankle joint.