Total articular resurfacing arthroplasty with the Tara device was performed on sixty-seven hips in sixty-three patients from 1978 to 1981. I analyzed the results, paying particular attention to prosthetic failure. Loosening of the femoral component occurred in one hip and loosening of the acetabular component, in seven hips. All eight required revision to conventional total hip replacement. Fifteen other patients in the series had radiographic evidence of component failure but have had no significant pain to date. They were regarded as having impending failure. Four of the fifteen showed significant stress-shielding on the femoral side, two with simultaneous acetabular lucency at the bone-cement interface. The other eleven showed progressive acetabular lucency. The total anticipated failure rate was 34.3 per cent (11.9 per cent definite and 22.4 per cent anticipated). The ages of the patients at surgery averaged 49.1 years in the actual failure group and 34.2 years in the impending failure group. Factors that may have been responsible for the unacceptably high incidence of component failure include the young age of the patients in whom this operation was performed and their high activity level. Additional reasons for mechanical failure (both definite and anticipated) on the acetabular side include poor cement distribution with resultant micromotion and increased frictional torque with the larger-diameter component of the prosthesis.