 Total Hip Arthroplasty THA is one of the most successful surgical interventions. Replacement of an arthritic hip joint provides significant pain relief and improvement of hip function and mobility. Patients, even elderly people, are more active, have a better quality of life, less comorbidities and a longer life expectancy. The World Health Organisation WHO has declared THA the second best intervention, only preceded by cataract surgery, regarding cost effectiveness and quality of outcome. In patients older than 70 years, the overall survivorship of THA is more than 90 at 10 years and the best clinical results are obtained for THA as a treatment for osteoarthritis OA. In this patient population, THA can thus be considered a lifelong solution. However, both survivorship and clinical results are much worse in young and active people. The reasons for this worse outcome are multiple. First of all, younger people usually have a more active lifestyle regarding work and sports. Secondly, the hip disorders leading to THA in a younger patient population are more difficult to treat. Congenital hip dysplasia is frequently associated with gross hip deformities, as may be the case in secondary traumatic OA. Bone stock may be jeopardised in cases of avascular necrosis of the femoral head AVN and rheumatoid arthritis RA. Thirdly, a faster bone metabolism may play a role, but this remains to be elucidated. 