PURPOSE: In the evaluation of acetebular fractures, conventional radiography is limited by distortion, magnification, and overlap of fracture fragments. Computed tomography(CT) has already been shown to be superior in this field. The purpose of this paper was to use 3D reformations for classification of acetabular fractures and planning of operation. MATERIALS AND METHODS: From July 1994 to December 1998, we reviewed 40 acetabular fractures. We evaluated fractures as plain X-ray(inlet & outlet view, AP view, obturator foramen & illiac wing view), axial CT with 3 mm slices, and 3D reformations. We classified fractures by classification of Letournel. RESULTS: 32 cases of 40 cases were displaced fractures, We recognized fracture easily in 3D reformations. 12 cases were posteior wall fracture. 9 cases were both column frctures. We interpretated both column fractures difficultly in plain X-ray, but we had many informations about rotation & displacement of fracture fragment by 3D reformations. Undisplaced fracture was 8 cases. We interpretated undisplaced fracture difficultly in 3D reformations and distinguished difficultly from normall 3D reformations. CONCLUSION: 3D reformations were useful for analysis of complex displaced fracture but not useful for analysis of undisplaced fracture. Acetabular internal oblique view was useful for analysis of quadrilateral space & posterior wall fractures. Acetabular external view was useful for decision of surgical approach.