Cementless total hip arthroplasty has become increasingly popular recently because of problems of aseptic loosening of cemented implants, especially in younger, more active patients. The threaded acetabular component design gains initial purchase by thread engagement and provides longterm macro-interlock fixation as bone consolidation occurs between the threads. But there was little clinical or experimental information about the aseptic loosening or cup migration of cementless acetabular fixation with threaded components. We did the radiological assessment of cup migration in 113 cementless hip arthroplasty performed at the Department of Orthopaedic Surgery, Catholic University Medical College, Kangnam St. Mary's Hospital during May 1974 to May 1989. The follow-up ranged from one year to 15 years, averaging 3 years and 8 months. The results were obtained as follows: 1. Radiolucent line around the cup (1mm or more) developed in 24 patients (21.2%) including cup migration cases. 2. Cup migration (2mm or more) developed in 17 patients (15.0%) out of 113 threaded cups. 3. Upward cup migration (average 7.7mm) complicated in all 7 patients, while medial migration (average 4.3mm) developed in 11 out of 17 patients. 4. Eight cases (32%) of cup migration developed in 25 ceramic cups, while 9 cases (10%) develeped in 88 metal backed polyethylene cups.5. Twenty-four cases had acetabular medial wall cortical breakage at the time of operation, and 10 (41.7%) out of these 24 cases developed cup migration. 6. Preoperative average Harris hip score of 53 became 88 postoperatively. But the patients who had loosening sign or cup migration had average preoperative hip score of 45 became 72 postoperatively. 7. Cup migration developed more often in the patients who had ceramic cup and/or breakage of inner cortex of acetabulum at the time of surgery. Through this study it was concluced that the truncated threaded cup has relatively high incidence of loosening, particularly the ceramic cup, and that the ceramic cup to ceramic head combination is not a good one.