The twenty-three cases of unstable Colles fracture were treated from Jan. 1994 to May 1998 at the department of orthopaedic surgery of Seoul Red Cross Hospital. Among them, the sixteen cases were treated with closed reduction with percutaneous pinning, others were treated with external fixator(Ace colles quadrilateral devices, USA). A retrospective study was made and evaluated using the Modification of Gartland and Werley's scoring system. The result of this study were as follow: 1. The ratio of male to female was 9 cases(39%) to 14 cases(61%). 2. The causes were falling down from a height 12 cases(50%), slip down 8 cases(35%) and traffic accident 3 cases(13%). 3. The reduction loss did not occur with the patients treated external fixation using Ace colles qredrilateral device, however three cases of the reduction loss have occurred with the patients using percuteneous pinning. 4. According to the Modification of Gartland and Werley's scoring system, the results of exteral fixation were excellent 4 cases(58%), good 1 case(14%), fair 1 case(14%) and poor 1 case(14%). and for percutoneous pinning, excellent 6 cases(38%), good 4 cases(25%), fair 2 cases(12%) and poor 4 cases(25%). 5. The complications of cases using external fixation were pin site infection 1 case and wrist stiffness 1 case, but for percutaneous pinning, reduction loss 3 cases. pin site infection 2 cases, wrist stiffness 2 cases, and decreased external rotation of forearm 3 cases.