Since the use of Charnley hip prosthesis, total hip arthroplasty has been used for the treatment of coxarthrosis. However, aseptic lossening of the acetabular cup component in total hip arthroplasty remains the most common cause of failure and most serious complication. Cementless acetabular cup fixation in total hip arthroplasty is increasingly popular because of the high failure rates of cemented components, particularly in younger and more active patients. We have experienced 62 cases of CLS expansion acetabular cup developed by L. Spontorno, from January 1992 to January 1994. We analysed 41 CLS expansion acetabular cup components in 38 patients performed at the Department of Orthopedic Surgery, Kang Nam General Hospital with minimum follow up lyear(average 17.3 months). The object of this study is to evaluate the radiographic change of the cup inclination, horizontal and vertical migration of the CLS expansion acetabular cup by methods of Engh et al, and Callagham et al. The results were as follows: 1. The initial adequate contact fit were 39 hips and inadequate fit in 2 hips. 2. The initial acetabular inclination between 35 degrees and 55 degrees were 38 hips. 3. Vertical and/or horizontal migration was not occurred, except 2 hips which were complicated by deep infection. 4. Change of acetabular cup inclination than 5 degrees were not occurred. 5. Radiolucent line wider than 2mm was not found. 6. In final follow up of out 41 hips optimal stability was obtained in 39 hips, suboptimal stability was obtained in 2 hips, and definite instability was not found.