Oxford medial unicompartmental arthroplasty (UCA) is now routinely performed through a short incision without dislocation of the patella. We present the 1 year results of the first 104 knees operated in Oxford using this technique and the learning curve associated with it. The patient's average age at surgery was 68 years. The average American Knee Society 'knee score' improved from 37 to 94 points and the average 'functional score' from 50 to 92 points. Average maximum flexion improved from 117 to 131 degrees. The average knee score during a surgeon's first 10 cases was 88 points, which was significantly less (P<0.03) than the score achieved for subsequent cases after the first 10 (95 points). These data suggest for the first time that a learning curve exists with worse results being achieved during a surgeon's first 10 cases. However, the results during the learning curve are still similar to that achieved after total knee arthroplasty.