This study examined the mid-term (more than 5 years) results of cementless total hip arthroplasty (THA) using Biomet acetabular cups (locking mechanism: Hexloc type or Ringloc type). A series of 58 patients (70 hips) who had undergone cementless THA at our department were available for inclusion in this study. The average age at surgery was 55.2 years, and the average follow-up was 6 years 10 months. Osteolysis occurred in five cases. In the group with osteolysis, the average annual linear wear was 0.18 mm/year, and in the group without osteolysis it was 0.10 mm/year. The higher linear wear rate in the osteolysis group was statistically significant compared to that in the nonosteolysis group. The age of the patient was closely related to polyethylene (PE) wear in the Hexloc group but not in the Ringloc group. In the Ringloc group there was no close correlation between the thickness of the PE liner and the average annual linear wear, whereas in the Hexloc group the thicker liner had significantly less annual linear wear. It was thought that PE wear of the Hexloc cup was more susceptible to the age of the patient at surgery and the PE thickness than that of the Ringloc cup owing to several structural differences, such as rotational stability and conformity between the metal cup and the PE liner.