The Knee Society scores and other outcome measures in patients aged 80 years or older (n = 51) who had mobile bearing unicompartmental knee arthroplasty performed in Tayside, Scotland, were reviewed retrospectively. The results were compared with those in younger age groups: "younger than 60 years" (n = 110), "60 to 69 years" (n = 164), and "70 to 79" years (n = 145). In the study group, the mean Knee Society knee score (objective) at 1-year follow-up was 85.21, compared with a mean of 77.82 for younger-than-60-years age group, 81.28 for 60-to-69-years age group, and 87.33 for 70-to-79-years age group. The differences between the knee scores in the study group and the other groups were not statistically significant. Revision rate and survival of implant were not different between the groups. We conclude that patients aged 80 or older should be considered for mobile bearing unicompartmental knee arthroplasty if they fulfill the described criteria.