We measured poiyethylene wear radiographically in 85 cementless primary total hip arthroplasties by the modified technique of Livermore et al. All the patients were followed up for at least five years (mean, 6.31 years; range, 5 years-8 years 2 months). The mean extent of linear wear was 0.88mm (range, 0.0083-3.2839mm), and the mean rate of linear wear was 0.14mm/year(range, 0.00-0.47mm /year). The mean volumetric wear was 539.42mm (range, 5.11 2022.09mm), and the mean rate of volumetric wear was 87.69mm/year(range, 0.65-290.12mm/year). The polyethylene wear was correlated inversely with the patients age only, but was not influenced by weight or gender of the patients, Harris hip score, thickness of the polyethylene, the abduction angle of acetahular cup, or the duration of in situ implantation. Osteolysis developed in the femur of 34 hips(40%) and in the acetabulum of 11 hips(12.9%). Radiographic loosening was found in one case in the femur and none in the acetabul pm. The extent of polyethylene wear was significantly correlated with frequencies and sizes of the osteolytic lesion and was not directly associated with radiographic loosening of the prostheses. Calcar resorption was observed in 39 hips(45.9%) and was not associated with polyethylene wear. These results indicated that polyethylene wear of primary total hip arthroplasty should be considered one of major causes of osteolysis and has no direct relationship with prosthesis loosening. To reduce the extent of polyethylene wear, the material characteristics of polyethylene should be improved or new, durable, articulating materials should be researched.