Fifteen patients (16 hips) with an ankylosed hip joint for a mean of 36 years (3.5 to 65), had their hips converted to a cementless Total Hip Replacement (THR). They were followed-up for a median of 10.75 years (5.0 to 19) with none lost to follow-up. All patients showed improved mobility and function post-operatively. The Harris Hip Score improved from 70 (SEM 3.4) to 83 post-operatively (SEM 4.4), which was statistically significant (p < 0.05). There was one acetabular cup revision at 5 years post implantation for aseptic loosening. All other femoral and acetabular components remained clinically and radiographically well fixed. We conclude that a previously ankylosed hip can be effectively converted to a cementless total hip replacement with good long term results.