BACKGROUND The treatment of isolated internal tibiofemoral knee osteoarthritis on young and active patients is controversial. This treatment can be a high tibial osteotomy or a joint replacement that can be a partial unicompartmental knee arthroplasty (UKA) or total knee replacement (TKR). The aim of our study is the long-term evaluation of functional outcome of partial unicompartmental knee arthroplasty (UKA) in elderly patients under than 60 years. METHODS This is a retrospective study of 25 unicompartmental knee arthroplasties in 22 patients, collected between1993 and 2003 whose age was less than 60 years. The minimum follow-up was 10 years. At last follow, an analysis of IKS score (International Knee Score) with assessment of both articular and functional components have been established. The Radiological score of Knee Society (KS) was used. RESULTS At mean 14.2 years (min: 10, max: 20), the mean of knee flexion was 110 °. The IKS function score going 47 points preoperatively to 77 points postoperatively and IKS score 40 points knee preoperatively to 94 points postoperative. The radiological assessment found a postoperative mean tibiofemoral mechanical axis of 174.8 ° (172 ° min, max 182 °). The survival of implants at 12 years postoperatively was 84%. The survival of the prostheses was de84 to 12%, with a revision for polyethylene wear, a second for conflict of the femoral component with tibia thorns responsible of chronic pain, a third revision for infection and two for osteoarthritis evolution. CONCLUSION The long-term evaluation of patients with a unicompartmental does not objective an obvious deterioration of outcome with a normal rate of revision comparatively to other series without particular difficulties during revision.