Int Orthop. 2008 Apr;32(2):203-8. Epub 2007 Feb 15. Wangen H, Lereim P, Holm I, Gunderson R, Reikerås O. It is well accepted that youth and high activity levels are among the factors that increase the risk of mechanical failure of total hip prostheses. However, there are few reports of long-term results in very young patients. In this study, we evaluated the results of total 49 hip replacements (THRs) using an uncemented total hip prosthesis in 44 patients (28 females) who were 30 years or younger (range: 15-30 years). The diagnosis was ostearthritis due to congenital dislocations in 28 patients, with the remaining patients having diagnoses of sequelae of fracture, infection, Calve-Legg-Perthes disease, avascular necrosis, chondrodystrophia and epiphyseal dysplasia. In all cases we used an uncemented straight stem fully coated with hydroxyapatite (HA). In 36 cases we used a hemispherical cup inserted with press fit, and in seven cases we used a hemispherical screw cup. The patients were evaluated ten to 16 years (mean: 13 years) after the operation by radiographic and clinical examinations, including the Harris Hip, WOMAC and EuroQol-5D scores. In a sub-group of nine patients with a unilateral prosthesis, the muscle strength of the quadriceps and hamstrings was tested using a Cybex 6000. None of the stems were revised at the follow-up examination, and all were classified as well integrated, with no signs of radiological loosening. Twenty-four hips had revision of the acetabular component due to mechanical failure. The Harris Hip score was, on average, 88 (range: 62-100), the WOMAC score 80 (range: 37-100) and the EuroQol score 0.68 (range: -0.14-1). Isokinetic muscle strength testing showed that seven of the nine tested patients were weaker on the operated side. In conclusion, we found mechanical failures at the acetabular side, but excellent results with a fully HA-coated femoral stem, with no revisions after ten to 16 years.