Aims: To assess the long-term results of the Oxford Uni-compartmental knee prosthesis for unicompartmental osteoarthritis and to discuss these results in comparison to other, scarce, long term follow-up. Methods: Sixty-þve medial and 6 lateral prostheses were placed in 67 patients. After an average of 10 years, they were evaluated with the Hospital for Special Surgery (HSS) knee score. Results: Fifteen patients died after a mean of 7 years, without need for revision. Eight prostheses were lost to follow-up. Ten (16%) revisions were noted: in 4 cases (6%) this was associated with an initially poor operative indication or a postoperative malalignment. The mean HSS score in 35 medial and 3 lateral prostheses was 164. (79% excellent or good, 10.5% moderate and 10.5% poor results) compared to 168 at 4.5-years of follow-up. There is no signiþcant difference between the score of patients older and patients younger than 65 years of age. Conclusions: Because this type of prosthesis preserves a maximum of bone stock and is revised to a total prosthesis without much difþculty it is the þrst choice prosthesis for medial unicompartmental osteoarthritis in the relatively young patient. In the light of other, very scarce long-term follow-up series, and compared to follow-up of total knee prostheses, the revision rate is high. Therefore, in spite of the very good and lasting HSS score in this group, this prosthesis is not the þrst choice in the elderly.