Aims: We have been alerted due to a high and early failure rate in total hip arthroplasties using metal-on-metal (Metasul?) bearings. Investigation on retrieved bearings at revision surgery should lead us to causes for early failures. Methods: 135 primary total hip arthroplasties in 118 patients (28 women and 90 men) with Metasul¨ bearing were implanted between 1992 and 1998. The mean age at implantation was 55 years (range, 29 to 84). In 105 cases a cementless MŸller SL cup and in 30 cases a MŸller Reinforcement Ring was used. Twelve out of 105 cases with a þne blasted SL cup needed a revision surgery after 34.9 months (range, 13 to 59). Qualitative histology was performed in all cases, quantitative metal analysis took place in two cases. The wear rate of the heads and their insert was measured and compared to former studies. Bony cylinders taken from the acetabular roof prior to primary implantation were histologically analyzed and compared to cup migration studies (EBRA). Results: Four cups and seven cemented titanium stems with tight cups were loose. In one case with polyarthritis both components had to be replaced. In one patient with cup loosening an impingement between neck and cup was found. In two patients histology showed diminution of bone-stock and in two cases no bony integration was observed. Conclusions: From twelve revision cases, we found only one where the metal-metal bearing is clearly responsible for the revision surgery. Metal-on-metal articulation seems to be promising if the component orientation is correct.