Posterior malleolar fractures are usually caused by an abduction or external rotation injury. indications for open reduction of the posterior malleolar fracture depend on its size and the amount of displacement. If the fragment of the posterior malleolus involves more than 25% to 30% of the articular surface, it should be treated by anatomical reduction and internal fixation. Authors analysed twenty-three patients of ankle fractures with the posterior malleolar fractures who were treated in Kangbuk Samsung Hospital between March 1993 and March 1997. Thirteen patients whose posterior malleolar fracture involved less than 30% of articular surface were treated conservatively (Group 1), while ten patients with involvement of more than 30% of articular surface were treated by open reduction and internal fixation. Among the ten patients treateed by open reduction, the five patients were indirectly fixed through anterior approach (Group 2), another five patients were directly fixed through posterior approach (Group 3). In group 1, the patients whose opsterior malleolus involved more than 25% of articular surface have unsatisfactory results compared to patients whose posterior malleolus involved less than 25% of articular surface(P<0.04). The results of the treatment were better in those directly fixed through posterior appproach than in those indirectly fixed through anterior approach regardless of size of the fragment(P<0.05).