The concept of surface replacement or cup arthroplasty has been studied clinically for two decades, but few long-term studies have been published as yet. At the county hospital of Bodø the THARIES (Total Hip Articular Replacement by Internal Eccentric Shells) system was employed as a routine from 1979-86. 109 consecutively operated hips were followed up by clinical examination and radiological studies after three months, and after one, five and ten years. A loosening frequency of 21% was found after five years and 68% after ten years. At other centres the technique has been reserved mainly for younger patients with potentially solid bone stock. In this study we found 85% failures in the group of patients younger than 60 years at the time of arthroplasty, and 84% in males after ten years of observation. The results indicate that this conserving system is not strong enough to resume bearing weight, and does not have adequate resistance to fatigue to withstand years of cyclic loading, especially with a high level of activity.